The ability to produce diacetyl from pyruvate and l-serine was studied in various strains of Pediococcus pentosaceus and Pediococcus acidilactici isolated from cheese. After being incubated on both substrates, only P. pentosaceus produced significant amounts of diacetyl. This property correlated with measurable serine dehydratase activity in cell extracts. A gene encoding the serine dehydratase (dsdA) was identified in P. pentosaceus, and strains that showed no serine dehydratase activity car...

The ability to produce diacetyl from pyruvate and l-serine was studied in various strains of Pediococcus pentosaceus and Pediococcus acidilactici isolated from cheese. After being incubated on both substrates, only P. pentosaceus produced significant amounts of diacetyl. This property correlated with measurable serine dehydratase activity in cell extracts. A gene encoding the serine dehydratase (dsdA) was identified in P. pentosaceus, and strains that showed no serine dehydratase activity carried mutations that rendered the gene product inactive. A functional dsdA was cloned from P. pentosaceus FAM19132 and expressed in Escherichia coli. The purified recombinant enzyme catalyzed the formation of pyruvate from L- and D-serine and was active at low pH and elevated NaCl concentrations, environmental conditions usually present in cheese. Analysis of the amino acid profiles of culture supernatants from dsdA wild-type and dsdA mutant strains of P. pentosaceus did not show differences in serine levels. In contrast, P. acidilactici degraded serine. Moreover, this species also catabolized threonine and produced alanine and α-aminobutyrate.

Several strains of non-citrate-metabolizing Pediococcus halophilus have previously been isolated from soy sauce mash or moromi. The factors controlling the metabolism of citrate in soy pediococci were studied. All the soy pediococcal strains tested which failed to decompose citrate did not possess citrate lyase [citrate (pro-3S)-lyase; EC 4.1.3.6] activity. In P. halophilus, citrate lyase was an inducible enzyme, and the optimum pH for activity was 7.0. The metabolism of citrate in P. halophi...

Full Text Available Listeria monocytogenes is a bacterium capable to adhere to the surfaces of equipment and utensils and subsequently form biofilms. It can to persist in the food processing environmental for extended periods of time being able to contaminate the final product. The aim of this study was to trace the contamination route of L. monocytogenes on a fresh mixed sausage processing line, from raw material to the final product. The isolates obtained were characterized by serotyping and molecular typing by pulsed-field gel electrophoresis (PFGE using the restriction enzymes ApaI and AscI. L. monocytogenes was detected in 25% of the samples. The samples of raw material were not contaminated, however, the microorganism was detected in 21% of the environmental samples (food contact and non-food contact, 20.8% of the equipments, 20% of the food worker's hands, 40% of the mass ready to packaging and in all the final products samples, demonstrating that the contamination of final product occurred during the processing and the importance of cross contamination. PFGE yielded 22 pulsotypes wich formed 7 clusters, and serotyping yielded 3 serotypes and 1 serogroup, however, the presence of serotypes 4b and 1/2b in the final product is of great concern for public health. The tracing of contamination showed that some strains are adapted and persisted in the processing environment in this industry.Listeria monocytogenes é uma bactéria com capacidade de formar biofilmes e de colonizar superfícies de equipamentos e utensílios. Esse microrganismo pode persistir por longos períodos em plantas de processamento de alimentos, sendo capaz de contaminar o produto final. O objetivo deste estudo foi traçar a rota de contaminação de L. monocytogenes em uma linha de processamento de lingüiça mista frescal, desde a matéria-prima até o produto final. Os isolados obtidos foram caracterizados por sorotipagem e por tipagem molecular, através de Pulsed Field Gel

Full Text Available Vaginal probiotics have an important role in preventing the colonization of the vagina by pathogens. This study aimed to investigate different formulations with Pediococcus pentosaceus SB83 (lyophilized powder and tablets with and without retarding polymer in order to verify its stability and antilisterial activity after manufacture and during storage. The bacteriocinogenic activity of P. pentosaceus SB83 against Listeria monocytogenes was evaluated in simulated vaginal fluid. Suspension of Pediococcus pentosaceus SB83 reduced the pathogen only after 2 h and the lyophilized bacteria after 24 h of contact, and, in the tablets, P. pentosaceus SB83 lost the antimicrobial activity. The pH of simulated vaginal fluid decreased for all the tested conditions. As lyophilized powder demonstrated better results concerning antimicrobial activity, this formulation was selected to evaluate the antilisterial activity during the 12 months of storage. During storage at room temperature, lyophilized bacteria totally inhibited the pathogen only until one month of storage. At 4°C, P. pentosaceus SB83 showed antimicrobial activity during all the time of storage investigated. Therefore, the better formulation of P. pentosaceus SB83 is the lyophilized powder stored at 4°C, which may be administered intravaginally as a washing solution.

Full Text Available The objective of this study is to evaluate the antilisterial effect of Pediococcus pentosaceus T1, which was isolated from kimchi, and to assess its potential for extending the shelf life of salmon and kimchi. Pediococcus pentosaceus T1 culture eff ectively inhibited proliferation of Listeria monocytogenes in a dose-dependent manner in a salmon-based medium. Antilisterial effect of the culture was stronger than that of nisin, an antibacterial peptide, as evidenced by lower minimum inhibitory concentration value (20 mg/mL compared to nisin (over 20 mg/mL. P. pentosaceus T1 culture also effectively inhibited the growth of Listeria in salmon fi llet. In particular, the culture (6 g per 100 mL showed a stronger inhibitory effect than sodium hypochlorite (0.2 mg/mL, a disinfectant used in food processing. In kimchi fermentation, the treatment with P. pentosaceus T1 culture suppressed changes of acidity and pH during maturation. The inhibitory eff ect of the culture on kimchi lactic acid bacteria, which include Leuconostoc mesenteroides and Lactobacillus sakei, led to a drastic decrease in maturation rates of kimchi. Moreover, sensory test on kimchi treated with P. pentosaceus T1 showed that the culture improved overall acceptability of kimchi, which can be observed in higher scores of sourness, texture, off-flavour and mouthfeel compared with untreated kimchi. The results of this study suggest that kimchi-derived P. pentosaceus T1 could be a potential antilisterial agent in fi sh products as well as a starter to control overmaturation of kimchi.

A Gram-positive, small coccus-shaped lactic acid bacterium, strain LMG 23999(T), was isolated from Argentinean wheat flour. 16S rRNA gene sequence analysis revealed that the phylogenetic position of the novel strain was within the genus Pediococcus, with Pediococcus stilesii, Pediococcus pentosaceus and Pediococcus acidilactici as its closest relatives (97.7, 97.3 and 96.9 % gene sequence similarity, respectively). Fluorescent amplified fragment length polymorphism fingerprinting of whole genomes and whole-cell protein electrophoresis confirmed the unique taxonomic status of the novel strain. DNA-DNA hybridizations, DNA G+C content determination, comparative sequence analysis of the pheS, rpoA and atpA genes and physiological and biochemical characterization demonstrated that strain LMG 23999(T) (=CCUG 54535(T)=CRL 776(T)) represents a novel species for which the name Pediococcus argentinicus sp. nov. is proposed. Multi-locus sequence analysis based on pheS, rpoA and atpA genes was found to be a suitable method for the identification of species of the genus Pediococcus.

The present study was aimed to evaluate the bio-control efficacy of Pediococcus pentosaceus isolated from traditional fermented dairy products originated from India, against the growth and zearalenone (ZEA...

Full Text Available Bacteriocin-producing (Bac+ lactic acid bacteria (LAB comprising selected strains of Lactobacillus curvatus, Lactococcus lactis, Pediococcus acidilactici, and Enterococcus faecium and thailandicus were examined for inhibition of Listeria monocytogenes during hotdog challenge studies. The Bac+ strains, or their cell-free supernatants (CFS, were grouped according to mode-of-action (MOA as determined from prior studies. Making a mixture of as many MOAs as possible is a practical way to obtain a potent natural antimicrobial mixture to address L. monocytogenes contamination of RTE meat products (i.e., hotdogs. The heat resistance of the bacteriocins allowed the use of pasteurization to eliminate residual producer cells for use as post-process surface application or their inclusion into hotdog meat emulsion during cooking. The use of Bac+ LAB comprising 3× MOAs directly as co-inoculants on hotdogs was not effective at inhibiting L. monocytogenes. However, the use of multiple MOA Bac+ CFS mixtures in a variety of trials demonstrated the effectiveness of this approach by showing a >2-log decrease of L. monocytogenes in treatment samples and 6–7 log difference vs. controls. These data suggest that surface application of multiple mode-of-action bacteriocin mixtures can provide for an Alternative 2, and possibly Alternative 1, process category as specified by USDA-FSIS for control of L. monocytogenes on RTE meat products.

Lactic acid bacteria have received increased attention as a potential food preservative due to their strong antagonistic activity against many food-spoilage and pathogenic organisms. Three Pediococcus species, P. acidilactici NCIM 2292 , P. pentosaceous. NCIM 2296 and P. cervisiae NCIM 2171, were evaluated for bacteriocin production. Inhibitory substance were produced during the late growth phase and maximum production occurred at 37 degrees after 36-48 h of incubation. Bacteriocins partially purified from these species by cold-acetone precipitation at 0 degrees C and cell adsorption desorption techniques have a broad inhibitory spectrum against microorganisms, including gram-negative bacteria such as Escherichia coli and Pseudomonas. Proteolytic enzymes inactivated these peptides, but amylase and lipase did not show any effect. The bacteriocins were stable over a wide pH range (3-8) and apparently most active at pH 4.0-5.0. They were heat-stable (1 h at approximately 80 degrees C and autoclaving) at pH 5.0. No loss in activity was observed when stored under refrigeration (4-8 degrees C). Tris-Tricine SDS-PAGE revealed the molecular masses of these peptides to be between 3.5 and 5.0 kDa.

Full Text Available Abstract Background Bacteriocin-producing lactic acid bacteria are commonly used as natural protective cultures. Among them, strains of the genus Pediococcus are particularly interesting for their ability to produce pediocin, a broad spectrum antimicrobial peptide with a strong antagonistic activity against the food-borne pathogen Listeria monocytogenes. Furthermore, there is increasing interest in isolating new bacteriocin-producing strains of human intestinal origin that could be developed for probiotic effects and inhibition of pathogenic bacteria in the gut. In this work, we typed a new strain, co-isolated from baby faeces together with a Bifidobacterium thermophilum strain, and characterized its proteinaceous compound with strong antilisterial activity. Results The newly isolated strain UVA1 was identified as a Pediococcus acidilactici by carbohydrate fermentation profile, growth at 50°C and 16S rDNA sequencing. The partially purified bacteriocin was heat resistant up to 100°C, active over a wide range of pH (2 to 9 and susceptible to proteolytic enzymes. The molecular weight, estimated by SDS-PAGE, was similar to that of pediocin AcH/PA-1 (4.5 kDa. P. acidilactici UVA1 harboured a 9.5-kb plasmid that could be cured easily, which resulted in the loss of the antimicrobial activity. Southern hybridization using the DIG-labelled pedA-probe established that the bacteriocin gene was plasmid-borne as for all pediocin described so far. Nucleotide sequence of the whole operon (3.5 kb showed almost 100 % similarity to the pediocin AcH/PA-1 operon. The mRNA transcript for pedA could be detected in P. acidilactici UVA1 but not in the cured derivative, confirming the expression of the pedA-gene in UVA1. Using a new real-time PCR assay, eleven out of seventeen human faecal samples tested were found to contain pedA-DNA. Conclusion We identified and characterised the first pediocin produced by a human intestinal Pediococcus acidilactici isolate and

The first isolation methods for the detection of Listeria spp. were generally based on the direct culture of samples on simple agar media, but isolation of the pathogenic Listeria monocytogenes was difficult. In time, new techniques were developed, based on a variety of selective and elective agents

A fatal case of endocarditis due to Listeria monocytogenes is reported. Case reports of endocarditis due to this organism are rare but indicate a higher mortality than with many other causes of bacterial endocarditis. The size of the problem may be underestimated because the organism has a "diphtheroid' appearance and may be incorrectly dismissed as a contaminant.

Two bacteriocinogenic strains of Pediococcus parvulus and one bacteriocinogenic Enterococcus mundtii strain were evaluated for their potential to control the growth of Listeria monocytogenes on refrigerated, modified atmosphere (MA) stored mungbean sprouts. These three strains, which were isolated from minimally-processed vegetables, were shown to grow in culture broth at 4, 8, 15 and 30 degrees C. However, only Ent. mundtii was capable of bacteriocin production at 4-8 degrees C. Examination of the growth of these strains on agar under 1.5% O2 in combination with 0, 5, 20 or 50% CO2 revealed significantly higher maximum specific growth rates for Ent. mundtii than for Pediococcus parvulus at CO2 concentrations below 20%, which are relevant for MA-storage of vegetables. Enterococcus mundtii was subsequently evaluated for its ability to control the growth of L. monocytogenes on vegetable agar and fresh mungbean sprouts under 1.5% O2/20% CO2/78.5% N2 at 8 degrees C. The growth of L. monocytogenes was inhibited by bacteriocinogenic Ent. mundtii on sterile vegetable-medium but not on fresh produce. However, mundticin, the bacteriocin produced by Ent. mundtii, was found to have potential as a biopreservative agent for MA-stored mungbean sprouts when used in a washing step or a coating procedure.

Full Text Available Abstract Background Lactic acid bacteria (LAB can be isolated from traditional milk products. LAB that secrete substances that inhibit pathogenic bacteria and are resistant to acid, bile, and pepsin but not vancomycin may have potential in food applications. Results LAB isolated from a range of traditional fermented products were screened for the production of bacteriocin-like inhibitory substances. A total of 222 LAB strains were isolated from fermented milk products in the form of fresh curds, dried curds, and ghara (a traditional flavor enhancer prepared from whey, and fermented cocoa bean. Eleven LAB isolates that produced antimicrobial substances were identified as Lactococcus lactis, Lactobacillus plantarum, and Pediococcus acidilactici strains by biochemical methods and 16S rDNA gene sequencing. Of these, the cell-free supernatant of Kp10 (P. acidilactici most strongly inhibited Listeria monocytogenes. Further analysis identified the antimicrobial substance produced by Kp10 as proteinaceous in nature and active over a wide pH range. Kp10 (P. acidilactici was found to be catalase-negative, able to produce β-galactosidase, resistant to bile salts (0.3% and acidic conditions (pH 3, and susceptible to most antibiotics. Conclusion Traditionally prepared fermented milk products are good sources of LAB with characteristics suitable for industrial applications. The isolate Kp10 (P. acidilactici shows potential for the production of probiotic and functional foods.

Pediococcus lolii NGRI 0510QT was isolated from ryegrass silage produced on Ishigaki Island, Okinawa Prefecture, Japan. Here we present a draft genome sequence for this strain, consisting of 103 contigs for a total of 2,047,078 bp, 2,154 predicted coding sequences, and a G+C content of 42.1%. PMID:23405350

As in recent years laboratory diagnostics of listeria has become part of food microbiology, the frequency of occurrence of the bacteria Listeria monocytogenes has been followed in various kinds of foods for a year. A total of 51 strains of L. monocytogenes (7.2%) was isolated from 700 kinds of samples (raw milk, pasteurized milk, meat surface, poultry, cheeses, thermally not treated meat products, food--industry machinery). As can be seen in Tab. I, the highest number of strains was isolated from meat surfaces (13.5%), followed by meat--industry machinery (12.72%), poultry (10%) and cheeses (5%). The lower numbers of strains were found out in thermally not treated meat products (3.8%) and in raw milk (3.3%). Pasteurized milk did not contain any strains. Our findings in raw milk (3.3%) and in pasteurized milk (0) are in agreement with the data cited e. g. by authors from the USA (Lovett et al., 1987), who mention the value of 4.2% in raw milk and the zero value in pasteurized milk. The percentage of strains monitored in cheeses (5%) can be evaluated as low as the assortment of investigated cheeses was small (all strains were isolated from soft ripening cheeses). German authors (Tham et al., 1988) speak about the 2.5% percentage of L. monocytogenes strains; this is in keeping with our findings. The findings in thermally not treated meat products (3.8%) can be evaluated as low although the number of strains found in raw meat was high.(ABSTRACT TRUNCATED AT 250 WORDS)

The study was conducted to evaluate the attachment of three lactic acid bacteria (LAB) strains and their combination in a cocktail, to stainless steel coupons from a deli slicer, and their ability to inhibit the attachment of Listeria monocytogenes. In a previous study, three LAB strains, Pediococcus acidilactici, Lactobacillus amylovorus, and Lactobacillus animalis, were isolated from ready-to-eat meat and exhibited antilisterial effect. In the study reported here, hydrophobicity tests were determined according to the method of microbial adhesion to solvent. The attachment of the cells was evaluated on stainless steel coupons from deli slicers. Extracellular carbohydrates were determined with a colorimetric method. Based on these tests, L. animalis exhibited the greatest hydrophobicity (26.3%), and its adherence increased sharply from 24 to 72 h, whereas L. amylovorus yielded the lowest hydrophobicity (3.86%) and was weakly adherent. Although P. acidilactici had moderate hydrophobicity (10.1%), it adhered strongly. The attached LAB strains produced significantly (P < 0.05) higher total carbohydrates than their planktonic counterparts did, which is an important characteristic for attachment. Three conditions were simulated to evaluate the ability of the LAB cocktail (10(8) CFU/ml) to competitively exclude L. monocytogenes (10(3) CFU/ml) on the surface of the coupons. The coupons were pretreated with the LAB cocktail for 24 h prior to the addition of L. monocytogenes, simultaneously treated with the LAB cocktail and L. monocytogenes, or pretreated with L. monocytogenes 24 h prior to the addition of the LAB cocktail. The LAB cocktail was able to reduce the attachment L. monocytogenes significantly (P < 0.05). The LAB cocktail indicated potential attachment on stainless steel and bacteriostatic activity toward L. monocytogenes attached on stainless steel, which indicates a possible role for LAB as a biosanitizer in the food industry.

Full Text Available Abstract Background Though important in the context of food microbiology and as potential pathogens in immuno-compromised humans, bacterial isolates belonging to the genus Pediococcus are best known for their association with contamination of ethanol fermentation processes (beer, wine, or fuel ethanol. Use of antimicrobial compounds (e.g., hop-compounds, Penicillin by some industries to combat Pediococcus contaminants is long-standing, yet knowledge about the resistance of pediococci to antimicrobial agents is minimal. Here we examined Pediococcus isolates to determine whether antibiotic resistance is associated with resistance to hops, presence of genes known to correlate with beer spoilage, or with ability to grow in beer. Results Lactic acid bacteria susceptibility test broth medium (LSM used in combination with commercially available GPN3F antimicrobial susceptibility plates was an effective method for assessing antimicrobial susceptibility of Pediococcus isolates. We report the finding of Vancomycin-susceptible Pediococcus isolates from four species. Interestingly, we found that hop-resistant, beer-spoilage, and beer-spoilage gene-harbouring isolates had a tendency to be more susceptible, rather than more resistant, to antimicrobial compounds. Conclusion Our findings indicate that the mechanisms involved in conferring hop-resistance or ability to spoil beer by Pediococcus isolates are not associated with resistance to antibiotics commonly used for treatment of human infections. Also, Vancomycin-resistance was found to be isolate-specific and not intrinsic to the genus as previously believed.

Background Though important in the context of food microbiology and as potential pathogens in immuno-compromised humans, bacterial isolates belonging to the genus Pediococcus are best known for their association with contamination of ethanol fermentation processes (beer, wine, or fuel ethanol). Use of antimicrobial compounds (e.g., hop-compounds, Penicillin) by some industries to combat Pediococcus contaminants is long-standing, yet knowledge about the resistance of pediococci to antimicrobial agents is minimal. Here we examined Pediococcus isolates to determine whether antibiotic resistance is associated with resistance to hops, presence of genes known to correlate with beer spoilage, or with ability to grow in beer. Results Lactic acid bacteria susceptibility test broth medium (LSM) used in combination with commercially available GPN3F antimicrobial susceptibility plates was an effective method for assessing antimicrobial susceptibility of Pediococcus isolates. We report the finding of Vancomycin-susceptible Pediococcus isolates from four species. Interestingly, we found that hop-resistant, beer-spoilage, and beer-spoilage gene-harbouring isolates had a tendency to be more susceptible, rather than more resistant, to antimicrobial compounds. Conclusion Our findings indicate that the mechanisms involved in conferring hop-resistance or ability to spoil beer by Pediococcus isolates are not associated with resistance to antibiotics commonly used for treatment of human infections. Also, Vancomycin-resistance was found to be isolate-specific and not intrinsic to the genus as previously believed. PMID:19735560

The hematometra is a nosological entity that may not always be attributed to an embryonic defect of the paramesonefros; cervical-vaginal infections such as etiological possibilities due to Listeria monocytogenes (Lm), cervix malignant neoplasias, iatrogenias due to endometrial ablation with Lasser, traumatic bloody uterine curetage and because of cervical cryocoagulation or electrocoagulation are also mentioned. The case to be reported is from a woman in reproductive stage, who is 32 years old, and had menarca at the age of 13, starting her sexual life at 31, not using any method to control her fertility. When having an eight-week amenorrhea after 8 months of marriage, she visited the doctor for assumed pregnancy, within the prenatal analysis a pelvic echographic study was requested, finding out images that we concluded as hematometra, having been drained and demonstrated the presence of LM by anti-Lm antibodies, being administered Azitromicina and Espiramicina.

Pediococcus species isolated from forage crops were characterized, and their application to silage preparation was studied. Most isolates were distributed on forage crops at low frequency. These isolates could be divided into three (A, B, and C) groups by their sugar fermentation patterns. Strains LA 3, LA 35, and LS 5 are representative isolates from groups A, B, and C, respectively. Strains LA 3 and LA 35 had intragroup DNA homology values above 93.6%, showing that they belong to the species Pediococcus acidilactici. Strain LS 5 belonged to Pediococcus pentosaceus on the basis of DNA-DNA relatedness. All three of these strains and strain SL 1 (Lactobacillus casei, isolated from a commercial inoculant) were used as additives to alfalfa and Italian ryegrass silage preparation at two temperatures (25 and 48 degrees C). When stored at 25 degrees C, all of the inoculated silages were well preserved and exhibited significantly (P ammonia-nitrogen content, gas production, and dry matter loss and significantly (P < 0.05) higher lactate content than the control, but silages inoculated with LS 5 and SL 1 were of poor quality. P. acidilactici LA 3 and LA 35 are considered suitable as potential silage inoculants.

Infection with Listeria monocytogenes is rare and mainly seen in immunosuppressed patients. Infection with L. monocytogenes has a mortality rate of 30%. We present a case report of L. monocytogenes bacteraemia and endocarditis in a 70-year-old man with several co-morbidities and following four...... major surgical procedures. This illustrates the findings and characteristics in one of the 16 patients who died in 2013 and 2014 this summer due to sausage-related L. monocytogenes infection....

In this study, we assessed the potential as silage additive of a bacteriocin produced by Pediococcus acidilactici Northern Regional Research Laboratory (NRRL) B-5627 (pediocin SA-1). Maize was inoculated either with a bacterial starter alone (I) or in combination with the bacteriocin (IP), and untreated silage served as control. We monitored the products of fermentation (ethanol, and lactic and acetic acids), the microbial population, and the presence of the indicator strain Listeria monocytogenes Colección Española de Cultivos Tipo (CECT) 4032 (1×10(5) cfu/g) after 1, 2, 5, 8, 16, and 30d of ensiling. Our results indicated antilisterial activity of the bacteriocin, anticipating the disappearance of L. monocytogenes in IP compared with I and control silages. The PCR-denaturing gradient gel electrophoresis analysis revealed the addition of the bacteriocin did not affect the bacterial communities of the spontaneous fermentation, and the inoculant-containing bacteria (Lactobacillus plantarum, Lactobacillus buchneri, and Enterococcus faecium) were found in addition to the bacterial communities of untreated maize silages in I and IP silages. Both treatments increased the concentration of antimicrobial compounds (acetic acid, ethanol, and 1,2-propanodiol) and led to lower residual sugar contents compared with the control, which would provide enhanced aerobic stability. The fact that the identified species L. plantarum, L. buchneri, and E. faecium produce some of these inhibitory compounds, together with their persistence throughout the 30d of fermentation, suggest these bacteria could actively participate in the ensiling process. According to these results, pediocin SA-1 could be used as an additive to control the presence of L. monocytogenes in maize silages selectively, while improving their fermentative quality and eventually their aerobic stability.

Lactic acid bacteria (LAB) have historically been used in food fermentations to preserve foods and are generally-recognized-as-safe (GRAS) by the FDA for use as food ingredients. In addition to lactic acid; some strains also produce bacteriocins that have been proposed for use as food preservatives. In this study we examined the inhibition of Listeria monocytogenes 39-2 by neutralized and non-neutralized bacteriocin preparations (Bac+ preps) produced by Lactobacillus curvatus FS47; Lb. curvatus Beef3; Pediococcus acidilactici Bac3; Lactococcus lactis FLS1; Enterococcus faecium FS56-1; and Enterococcus thailandicus FS92. Activity differences between non-neutralized and neutralized Bac+ preps in agar spot assays could not readily be attributed to acid because a bacteriocin-negative control strain was not inhibitory to Listeria in these assays. When neutralized and non-neutralized Bac+ preps were used in microplate growth inhibition assays against L. monocytogenes 39-2 we observed some differences attributed to acid inhibition. A microplate growth inhibition assay was used to compare inhibitory reactions of wild-type and bacteriocin-resistant variants of L. monocytogenes to differentiate bacteriocins with different modes-of-action (MOA) whereby curvaticins FS47 and Beef3, and pediocin Bac3 were categorized to be in MOA1; enterocins FS92 and FS56-1 in MOA2; and lacticin FLS1 in MOA3. The microplate bacteriocin MOA assay establishes a platform to evaluate the best combination of bacteriocin preparations for use in food applications as biopreservatives against L. monocytogenes.

Pediocin PA-1 is a bacteriocin which is produced by Pediococcus acidilactici PAC1.0. We demonstrate that pediocin PA-1 kills sensitive Pediococcus cells and acts on the cytoplasmic membrane. In contrast to its lack of impact on immune cells, pediocin PA-1 dissipates the transmembrane electrical

Pediocin PA-1 is a bacteriocin which is produced by Pediococcus acidilactici PAC1.0. We demonstrate that pediocin PA-1 kills sensitive Pediococcus cells and acts on the cytoplasmic membrane. In contrast to its lack of impact on immune cells, pediocin PA-1 dissipates the transmembrane electrical pote

Full Text Available Bacteriocin producing Lactobacillus acidophilus and Pediococcus acidilactici were isolated from milk and meat samples, respectively. An attempt was made to produce bacteriocin in a Dairy Based (DB medium using these organisms. Higher bacteriocin activity was shown by L. acidophilus in the DB medium. Bacteriocins of both the organisms were effective against food pathogens. The bacteriocins were stable at pH 3 - 9 up to 24 h and active at 100ºC. The bacteriocins could be stored at -20ºC for at least 45 days, at 4ºC for 20 days and at 37ºC for 5 days.

Listeria monocytogenes is not a rare pathogen causing meningitis, mainly in small children and in close contacts to livestock. The pathogen is naturally resistant to cephalosporins and some glycopeptides as well, therefore despite of syndromologic diagnosis of meningitis and initial therapy with 3rd generation cephalosporins according to the guidelines therapeutic failures with clinical consequences may occur.

There are two ways in which bacteria survive killing by antibiotics. The most well-known, is antibiotic resistance, which results from the acquisition of a resistance gene or mutation that allows bacteria to grow and divide in the presence of antibiotic concentrations that would normally kill other...... that are completely refractory to antibiotics due to the inactivity of cellular processes. Persister cells have been linked to treatment failures in several bacterial infections including Mycobacterium tuberculosis, Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli. Preceding the start of this Ph......D project, Listeria monocytogenes was observed to form these antibiotic tolerant persister cells. L. monocytogenes is a Gram-positive, foodborne pathogen that causes listeriosis, a rare, but often lethal disease, even with antibiotic treatment. It typically affects pregnant women, neonates, the elderly...

Full Text Available Pediococcus pentosacues strains, isolates from naturally fermenting millet and buckwheat sourdoughs, were used as starters for millet and buckwheat sourdoughs fermentation in order to evaluate their metabolic activity in native sourdough environment. For comparison, fermentation of studied non-wheat sourdoughs with a wheat isolate was done. Generally, sourdoughs fermented with autochthonous isolates are characterized by higher value of TTA and lactic acid compared to sourdoughs fermented with wheat isolates. The observed differences in TTA value between the sourdoughs prepared with autochthonous pediococci and the ones with wheat isolate were more pronounced in the case of millet sourdoughs. Glucose concentration and lactic acid production varied depending on the used pediococci strains and fermentation time.

The proteolysis in grass carp sausages inoculated with Lactobacillus plantarum ZY40 and Pediococcus pentosaceus GY23 was investigated. As fermentation progressed, sarcoplasmic and myofibrillar proteins in both sausages were obviously degraded, and the proteolytic process was more intense in sausages inoculated with P. pentosaceus GY23. The increases in α-amino nitrogen, trichloroacetic acid (TCA)-soluble peptides and free amino acids were also detected in both sausages. The differences in α-amino nitrogen content and free amino acids concentration were due to the activity of inoculated lactic acid bacteria, while endogenous enzymes contributed to the release of TCA-soluble peptides. Our findings indicate that lactic acid bacteria influence proteolytic characterisation in fermented fish sausage, with strain-dependent activity.

Abstract Background Though important in the context of food microbiology and as potential pathogens in immuno-compromised humans, bacterial isolates belonging to the genus Pediococcus are best known for their association with contamination of ethanol fermentation processes (beer, wine, or fuel ethanol). Use of antimicrobial compounds (e.g., hop-compounds, Penicillin) by some industries to combat Pediococcus contaminants is long-standing, yet knowledge about the resistance of pediococci to ant...

caesarean-delivered, colostrum-deprived term piglets on parenteral nutrition for the first 15 h, were used as models for sensitive newborn infants. A commercially available probiotic strain, Lactobacillus paracasei F19 (LAP, 2·6x108 colony-forming units (CFU)/kg per d) and a novel LAB isolate, Pediococcus...... increased diarrhoea and density of F18 in the intestinal mucosa (Prelative to F18 alone (P

Identification of the beer-spoilage Lactobacillus and Pediococcus bacteria has largely taken two approaches; identification of spoilage-associated genes or identification of specific species of bacteria regardless of ability to grow in beer. The problem with these two approaches is that they are either overly inclusive (i.e., detect all bacteria of a given species regardless of spoilage potential) or overly selective (i.e., rely upon individual, putative spoilage-associated genes). Our goal was to design a method to assess the ability of Lactobacillus and Pediococcus to spoil beer that is independent of speciation or genetic background. In searching for a method by which to differentiate between beer-spoilage bacteria and bacteria that cannot grow in beer, we explored the ability of lactobacilli and pediococci isolates to grow in the presence of varying concentrations of hop-compounds and ethanol in broth medium versus on agar medium. The best method for differentiating between bacteria that can grow in beer and bacteria that do not pose a threat as beer-spoilage organisms was found to be a hop-gradient agar plate containing ethanol. This hop-gradient agar plate technique provides a rapid and simple solution to the dilemma of assessing the ability of Lactobacillus and Pediococcus isolates to grow in beer, and provides new insights into the different strategies used by these bacteria to survive under the stringent conditions of beer.

Listeria monocytogenes has been recognized as an important pathogen in immunocompromised patients, but it has been rarely reported in Taiwan. We reviewed 13 cases of L. monocytogenes bacteremia at National Taiwan University Hospital over a 12-year period. All of the patients had underlying diseases. Fever was the most common presenting symptom, and neurologic signs were found in 6 patients. Most of the patients received penicillin G, ampicillin or piperacillin with an aminoglycoside. Corticosteroids were used in 9 of 13 patients. The overall mortality directly due to L. monocytogenes bacteremia was 31%. However, patients treated with cephalosporins or oxacillin had higher mortality than those treated with penicillin G, ampicillin or piperacillin (p = 0.05). Given the increasing number of immunosuppressed patients in Taiwan, it is likely that more cases will be encountered. Physicians in Taiwan should be aware of L. monocytogenes bacteremia and its treatment.

Both in Europe and worldwide cheese has caused important outbreaks of listeriosis and can be a vehicle for transmission of Listeria monocytogenes to consumers. A systematic review and meta-analysis were conducted using scientific literature and European Food Safety Authority (EFSA) reports...... understanding of L. monocytogenes prevalence in different types of cheeses and provided results that can be useful as input for quantitative microbiological risk assessment modelling....

In recent years, tree fruits have emerged as a new concern for Listeria monocytogenes contamination. The objective of the current study was to evaluate the potential internalization of L. monocytogenes from the surface of avocados into the edible portions of the fruit during certain postharvest practices simulated in a laboratory setting. One set of intact avocados was spot inoculated with L. monocytogenes on the stem scar, and the second set was hydrocooled in water contaminated with L. monocytogenes. Under these experimental conditions, L. monocytogenes internalized into the avocado pulp through the stem or stem scar after both spot inoculation and hydrocooling. In avocados spot inoculated with 50, 130, 500, and 1,300 CFU per fruit, bacteria were detected in the edible portion adjacent to the stem scar within 15 days postinoculation during storage at 4°C. In avocados hydrocooled in water containing L. monocytogenes at 10(6) and 10(8) CFU/ml, bacteria reached the bottom end of the fruit, and the populations in the edible portion adjacent to the stem scar reached up to 5.90 to 7.19 log CFU/g within 10 to 15 days during storage at 4°C. Dye mixed with inoculum was useful for guiding subsequent sampling, but dye penetration patterns were not always consistent with bacterial penetration.

Full Text Available Shigellosis caused by Shigella is prevalent throughout the world with approximately 164.7 million cases, of which 163.2 million are in developing countries as per the World Health Organization report. In the current study the effect of a known Probiotic Lactic acid Bacteria (PLB Pediococcus pentosaceus, a previously reported strain of PLB from our laboratory on gastroenteric pathogen – Shigella dysenteriae was studied and its mode of action was established. In agar diffusion tests PLB lysate showed larger inhibition zones of S. dysenteriae than a known Shigella susceptible antibiotic ampicillin which shows a better potentiality of PLB lysate over standard antibiotic. Further the effect of PLB lysate on Shigella dysenteriae lysis was confirmed by electrophoretic and microscopic study. PLB lysate at 250 μg/mL protein concentration inhibited ~70% of Shigella dysenteriae growth in vitro. A significant protection was observed against the cellular damage caused by Shigella dysenteriae lysate. Red blood cells and buccal cells protection against the lysis induced by Shigella dysenteriae lysate substantiated the cytoprotective role of PLB, thus PLB can be an effective natural agent against Shigella mediated infection.

A tripeptidase was purified from the cytoplasm of Pediococcus pentosaceus K9.2 by anion-exchange chromatography, gel filtration chromatography, and high-performance liquid chromatography. The molecular mass of the enzyme was estimated by gel filtration at 100,000 Da. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified peptidase showed one protein band of 45,000 Da. Optimal enzyme activity was obtained at pH 7.0 and at 50 degrees C. The peptidase hydrolyzed all tripeptides tested. Cleavage was not observed with dipeptides, oligopeptides, or amino acid-p-nitroanilide derivatives. Strong inhibition of activity was caused by EDTA, 1,10-phenanthroline, dithiothreitol, and beta-mercaptoethanol, whereas phenylmethylsulfonyl fluoride and sulfur-reactive reagents had no effect on peptidase activity. Mg2+, Mn2+, and Ca2+ stimulated the hydrolyzing activity of the enzyme. The 20 N-terminal amino acids of the tripeptidase from P. pentosaceus had 84% identity with those from the corresponding N-terminal region of the tripeptidase from Lactococcus lactis subsp. cremoris Wg2.

Owing to its flavoring, antimicrobial, antioxidant and anticarcinogenic nature, vanillin is widely used in foods, beverages, perfumes and pharmaceutical products. Ferulic acid (FA) is an important precursor of vanillin which is abundant in cereals like maize, rice and wheat and sugar beet. A major drawback of microbial vanillin production from FA is the degradation and biotransformation of toxic vanillin to other phenolic derivatives. The present study is undertaken to explore microbial vanillin production from FA precursor rice bran by employing vanillin-resistant Pediococcus acidilactici BD16, a natural lactic acid bacteria isolate. Extracellular, intracellular and cellular vanillin dehydrogenase activity was found least, which was minimized vanillin degradation, and the strain resists more than 5 g L(-1) vanillin in the medium. A metabolomics approach was followed for the detection of FA, vanillin and other metabolites generated during fermentation of rice bran medium. A metabolic pathway was also predicted for vanillin biosynthesis. Approximately 1.06 g L(-1) of crude vanillin was recovered from rice-bran-containing medium and this further offers scope for the industrial utilization of the organism and its genetic manipulation to enhance production of biovanillin.

The application of probiotics in aquaculture has received concerted research efforts but the localised intestinal immunological response of fish to probiotic bacteria is poorly understood. Therefore, a study was conducted to evaluate the probiotic effect of Pediococcus acidilactici on Nile tilapia (Oreochromis niloticus) with specific emphasis on intestinal health and probiotic levels as well as system level responses such as growth performance, feed utilization and haemato-immunological parameters under non-challenged conditions. Fish (9.19 ± 0.04 g) were fed either a control diet or a P. acidilactici supplemented diet (at 2.81 × 10(6) CFU g(-)(1)) for six weeks. At the end of the study the probiotic was observed to populate the intestine, accounting for ca. 3% (1.59 × 10(5) CFU g(-)(1)) of the cultivable intestinal bacterial load. Real-time PCR indicated that the probiotic treatment may potentiate the immune-responsiveness of the intestine as up-regulation of the gene expression of the pro-inflammatory cytokine TNFα was observed in the probiotic fed fish (P 0.05).

Full Text Available Authors report a fatal neonatal sepsis caused by Listeria monocytogenes. While the diagnostic procedure aimed to identify the microrganism is described, it is emphasized the importance to recover Streptococcus agalactiae (GBS and L. monocytogenes by means of vaginal-rectal swab culture. The intrapartum screening for L. monocytogenes, by Polymerase Chain Reaction (PCR providing results in 75 minutes is also evaluated.

Direct-fed microbials (DFM), general y regarded as safe status, are successful y used in improving rumen ecology, gastro-in-testinal health, feed efifciency, milk production and growth rate in ruminants. On the other hand, methanogenesis in rumen, which accounts for a signiifcant loss of ruminant energy and increased greenhouse gas in environment, is of great concern, therefore, use of DFM for improving productivity without compromising the animal health and ecological sustainability is encouraged. The present study was conducted to investigate the methane reducing potential of bacteriocinogenic strain Pediococcus pentosaceus-34. Since, the culture showed no hemolysis on blood agar and DNase activity, hence, it was considered to be avirulent in nature, a prerequisite for any DFM. The culture also showed tolerance to pH 5.0 for 24 h with 0.5%organic acid mixture, whereas when given a shock for 2 h at different pH and organic acids concentrations, it showed growth at pH 3.0 and 4.0 with 0.1 and 1.0%organic acids, respectively, as having good animal probiotics attributes. The total gas production was signiifcantly (P<0.05) higher in live pedicoccal culture (LPC) and dead pedicoccal culture (DPC) both with wheat straw, when compared to the control. In sugarcane bagasse, gas production was signiifcantly lower (P<0.05) with LPC compared to the control and DPC both. Methane was reduced by the inclusion of LPC in sugarcane bagasse (0.07 mL CH4 mg–1 dry matter digestibility) with no effect on other rumen fermentation parameters. However, with wheat straw and LPC total gas, in vitro dry matter digestibility, total volatile fatty acids increased signiifcantly but no reduction in methane production was observed in comparison to the control. Therefore, further research is warranted in this direction, if the bacteriocinogenic strains can be used as DFM for ruminants to improve the ruminant productivity.

Cell growth and pediocin production by Pediococcus acidilactici NRRL B-5627 on whey were compared by using batch fermentation and re-alkalized fed-batch fermentation. The batch fermentations were performed on DWG [DW (diluted whey) supplemented with 1% (w/v) glucose], DWYE [DW supplemented with 2% (w/v) yeast extract] and DWGYE (DW supplemented with 1% glucose plus 2% yeast extract) media. The fed-batch culture on DWYE medium was fed with a mixture of concentrated whey (48 g of total sugars/l) supplemented with 2% yeast extract and 400 g/l concentrated glucose. The re-alkalized fed-batch culture was characterized by higher biomass (6.57 g/l) and pediocin [517.6 BU (bacteriocin activity units)/ml] concentrations compared with the batch processes on MRS (de Man, Rogosa and Sharpe) broth (1.76 g/l and 493.2 BU/ml), DW (0.17 g/l and 57.7 BU/ml), DWG (0.14 g/l and 53.6 BU/ml), DWYE (1.43 g/l and 187.6 BU/ml) and DWGYE (1.28 g/l and 167.3 BU/ml) media. A mixed acid fermentation was observed during the growth of P. acidilactici NRRL B-5627 in the fed-batch culture on DWYE medium, and other products (acetic acid and ethanol) in addition to lactic acid accumulated in the medium. Mathematical models were set up to describe fed-batch production of biomass and pediocin by P. acidilactici. The models developed offer a better fit and a more realistic description of the experimental biomass and pediocin production data when compared with the logistic and Luedeking and Piret model.

Uterine infections in dairy cows lower profitability of dairy operations. Infections of the reproductive tract are related to the overgrowth of pathogenic bacteria during the first three weeks after parturition. However, alterations in the vaginal microbiota composition in the first weeks after parturition remain poorly documented. In this study, bacteria isolated from the vagina of healthy pregnant, and infected postpartum cows were characterised by random amplification of polymorphic DNA (RAPD) analysis and partial 16S ribosomal RNA (rDNA) gene sequencing. Populations of bacilli and lactic acid bacteria of the genera Enterococcus, Lactobacillus, and Pediococcus were present in both healthy and infected cows. Infected cows had a significant increase in the vaginal enteric bacteria population which consisted mainly of Escherichia coli. Three E. coli isolates harboured the gene coding for Shiga-like-toxin (SLT) I or II. Several isolates of the Pediococcus acidilactici were found to produce the bacteriocin pediocin AcH/PA-1. Quantitative PCR analyses of vaginal mucus samples collected from ten metritic cows before and after parturition confirmed the presence of the Lactobacillus group (Lactobacillus spp., Pediococcus spp., Leuconostoc spp., and Weissella spp.); Enterobacteriaceae, E. coli, and bacilli. The presence of the pediocin AcH/PA-1 structural gene and SLT genes were also confirmed with qPCR. In conclusion, overgrowth of pathogenic bacteria, particularly E. coli, after parturition likely contributes to the development of metritis. Our microbiota analysis extends the information related to the composition of commensal bacteria in the bovine female reproductive tract and may facilitate the development of novel intervention strategies for prevention of uterine infections in dairy cows.

Full Text Available Abstract Background Uterine infections in dairy cows lower profitability of dairy operations. Infections of the reproductive tract are related to the overgrowth of pathogenic bacteria during the first three weeks after parturition. However, alterations in the vaginal microbiota composition in the first weeks after parturition remain poorly documented. Results In this study, bacteria isolated from the vagina of healthy pregnant, and infected postpartum cows were characterised by random amplification of polymorphic DNA (RAPD analysis and partial 16S ribosomal RNA (rDNA gene sequencing. Populations of bacilli and lactic acid bacteria of the genera Enterococcus, Lactobacillus, and Pediococcus were present in both healthy and infected cows. Infected cows had a significant increase in the vaginal enteric bacteria population which consisted mainly of Escherichia coli. Three E. coli isolates harboured the gene coding for Shiga-like-toxin (SLT I or II. Several isolates of the Pediococcus acidilactici were found to produce the bacteriocin pediocin AcH/PA-1. Quantitative PCR analyses of vaginal mucus samples collected from ten metritic cows before and after parturition confirmed the presence of the Lactobacillus group (Lactobacillus spp., Pediococcus spp., Leuconostoc spp., and Weissella spp.; Enterobacteriaceae, E. coli, and bacilli. The presence of the pediocin AcH/PA-1 structural gene and SLT genes were also confirmed with qPCR. Conclusions In conclusion, overgrowth of pathogenic bacteria, particularly E. coli, after parturition likely contributes to the development of metritis. Our microbiota analysis extends the information related to the composition of commensal bacteria in the bovine female reproductive tract and may facilitate the development of novel intervention strategies for prevention of uterine infections in dairy cows.

Listeria monocytogenes contamination of seafood varies with product category. The highest prevalence was found in cold- smoked fish (34-60%), while the lowest was found in heat- treated and cured seafood (4-12%). The prevalence of L. monocytogenes differed greatly in cold-smoked salmon between...... production sites, ranging from monocytogenes. The organism showed moderate growth...... in naturally contaminated cold-smoked, and 'gravad', fish while the growth appeared faster in hot smoked fish. Thus L. monocytogenes is not under control in these products. Finally, the prevalence and growth of L. monocytogenes in naturally contaminated cold-smoked salmon are discussed in relation...

Listeria monocytogenes contamination of seafood varies with product category. The highest prevalence was found in cold- smoked fish (34-60%), while the lowest was found in heat- treated and cured seafood (4-12%). The prevalence of L. monocytogenes differed greatly in cold-smoked salmon between...... production sites, ranging from monocytogenes. The organism showed moderate growth...... in naturally contaminated cold-smoked, and 'gravad', fish while the growth appeared faster in hot smoked fish. Thus L. monocytogenes is not under control in these products. Finally, the prevalence and growth of L. monocytogenes in naturally contaminated cold-smoked salmon are discussed in relation...

A practical system was devised for grouping bacteriocins of lactic acid bacteria (LAB) based on mode of action as determined by changes in inhibitory activity to spontaneously-acquired bacteriocin resistance (Bac(R)). Wild type Listeria monocytogenes 39-2 was sensitive to five bacteriocins produced by 3 genera of LAB: pediocin PA-1 and pediocin Bac3 (Pediococcus), lacticin FS97 and lacticin FS56 (Lactococcus), and curvaticin FS47 (Lactobacillus). A spontaneous Bac(R) derivative of L. monocytogenes 39-2 obtained by selective recovery against lacticin FS56 provided complete resistance to the bacteriocin made by Lactococcus lactis FS56. The lacticin FS56-resistant strain of L. monocyotgenes 39-2 was also cross-resistant to curvaticin FS47 and pediocin PA-1, but not to lacticin FS97 or pediocin Bac3. The same pattern of cross-resistance was also observed with Bac(R) isolates obtained with L. monocytogenes Scott A-2. A spontaneous mutation that renders a strain cross-resistant to different bacteriocins indicates that they share a common mechanism of resistance due to similar modes of action of the bacteriocins. Spontaneous resistance was acquired to other bacteriocins (in aggregate) by following the same procedure against which the Bac(R) strain was still sensitive. In subsequent challenge assays, mixtures of bacteriocins of different modes of action provided greater inhibition than mixtures of bacteriocins of the same mode of action (as determined by our screening method). This study identifies a methodical approach to classify bacteriocins into functional groups based on mechanism of resistance (i.e., mode of action) that could be used for identifying the best mixture of bacteriocins for use as biopreservatives.

Listeria monocytogenes can survive and grow in refrigerated foods with pH values of approximately 4.0 to 5.0 and salt concentrations of 3 to 4%. Home-fermented refrigerator dill pickles fit this description. Contamination of this product with L. monocytogenes could cause serious problems because these items are not heated prior to consumption. L. monocytogenes survival and growth patterns were investigated in refrigerator dill pickles at 1.3, 3.8, and 7.6% salt concentrations. Pickling cucumbers were dipped into an inoculum of L. monocytogenes, brine mixtures were added, and cucumbers were held at room temperature for 1 week and then refrigerated for up to 3 months. The pH, NaCl percentage, titratable acidity percentage, and total populations of Listeria and aerobic, psychrotrophic, and lactic acid bacteria were measured at the addition of brine, after 2, 4, and 7 days of storage at room temperature, and then weekly during refrigerated storage. The initial Listeria population was 5.4 to 5.6 log CFU/cm2 on cucumber surfaces and 3.9 to 4.6 log CFU/g internally. There was an approximate 0.3- to 1-log increase during room temperature fermentation followed by a population decline during refrigerator storage, with a greater decrease in the brines with the highest NaCl concentration. Up to 49 days, the internal tissue of pickles with 1.3, 3.8, or 7.6% salt concentrations were presumptively positive for L. monocytogenes by the enrichment method, and at 91 days the surfaces of such pickles were still positive for L. monocytogenes. Populations of total aerobes and lactic acid bacteria increased during room temperature storage and decreased gradually during refrigerated storage.

Full Text Available Dry sausages have been considered ready-to-eat products with low risk of causing listeriosis due to the hurdles created during the manufacturing process such as low pH and a w, high salt concentration and presence of lactic acid bacteria (LAB. However, several studies have detected survival of Listeria monocytogenes in these products and also shown that process parameters, LAB and L. monocytogenes strains directly influence the results. In this work, survival of the pathogen in sausages prepared with three different formulations (one standard formulation, one formulation added of Lactobacillus plantarum and one added of 2% sodium lactate, using the manufacturing process usually employed in Brazil, was evaluated. Naturally contaminated sausages presented a small increase in the counts of L. monocytogenes in the first days of the process, followed by a gradual decrease until the end of the process. In experimentally contaminated samples containing L. plantarum, the reduction of counts of L. monocytogenes during processing was considerable, but there wasn´t significant differences between the treatments.Salames têm sido considerados produtos prontos para o consumo com baixo risco de provocar listeriose devido aos obstáculos criados no processo de fabricação e suas características de pH e atividade água baixos, alta concentração de sal e presença de bactérias lácticas. Entretanto, a sobrevivência de Listeria monocytogenes nesta classe de produtos é verificada e estudos de processo visando à redução da contaminação por este patógeno, têm demonstrado que particularidades como variação dos parâmetros de processo, cepas de bactérias lácticas e de L. monocytogenes influenciam diretamente os resultados. Neste estudo três formulações foram avaliadas (uma padrão, uma com inoculação da cultura Lactobacillus plantarum e outra com adição 2% de lactato de sódio empregando parâmetros de processo comumente praticados no Brasil

Full Text Available The objectives of this research were to study taxonomical status of lactic acid bacteria (LAB isolated from broiler and adherence ability on mucus in vitro. Molecular analysis was performed by analyzing 16S rRNA gene using universal primer. The adherence assay on mucus was carried out using microplate method with total plate count (TPC, absorbance (A550 and confirmed by scanning electron microscopy (SEM. The results of this studies revealed that three of LAB isolates have closed relation to Pediococcus acidilactici (99.9% species.Three isolates of P. acidilactici have adherence ability on broiler mucus higher than that on porcine mucin with an adherence percentage of 55.5% versus 50.8% and absorbance A550 of 0.061 versus 0.051, respectively. The highest adherence ability showed by P. acidilactici R02 with adherence percentage was 59.3% and absorbance A550 = 0.068. Adherence on mucus were affected by the addition of 3 g/l of gastric juice and 0.3% (b/v of bile salt. Adherence analysis using SEM also showed that the adherence on broiler mucus was higher than the adherence on porcine mucin. Altogether this adherence studies, suggest that three isolates of P. acidilactici LAB were capable of colonizing host intestinal mucus in vitro as important property to be promising probiotic bacteria for broiler.Key words : adherence, broiler, Pediococcus, mucus, 16S rRNA

The present study was aimed to evaluate the bio-control efficacy of Pediococcus pentosaceus isolated from traditional fermented dairy products originated from India, against the growth and zearalenone (ZEA) production of Fusarium graminearum. The cell-free supernatants of P. pentosaceus (PPCS) were prepared and chemical profiling was carried out by GC-MS and MALDI-TOF analysis. Chemical profiling of PPCS evidenced that, the presence of phenolic antioxidants, which are responsible for the antifungal activity. Another hand, MALDI-TOF analysis also indicated the presence of antimicrobial peptides. To know the antioxidant potential of PPCS, DPPH free radical scavenging assay was carried out and IC50 value was determined as 32 ± 1.89 μL/mL. The antifungal activity of P. pentosaceus was determined by dual culture overlay technique and zone of inhibition was recorded as 47 ± 2.81%, and antifungal activity of PPCS on F. graminearum was determined by micro-well dilution and scanning electron microscopic techniques. The minimum inhibitory concentration (MIC) of PPCS was determined as 66 ± 2.18 μL/mL in the present study. Also a clear variation in the micromorphology of mycelia treated with MIC value of PPCS compared to untreated control was documented. Further, the mechanism of growth inhibition was revealed by ergosterol analysis and determination of reactive oxygen species (ROS) in PPCS treated samples. The effects of PPCS on mycelial biomass and ZEA production were observed in a dose-dependent manner. The mechanism behind the suppression of ZEA production was studied by reverse transcriptase qPCR analysis of ZEA metabolic pathway genes (PKS4 and PKS13), and results showed that there is a dose dependent down-regulation of target gene expression in PPCS treated samples. The results of the present study were collectively proved that, the antifungal and ZEA inhibitory activity of PPCS against F. graminearum and it may find a potential application in agriculture and food

The present study was aimed to evaluate the bio-control efficacy of Pediococcus pentosaceus isolated from traditional fermented dairy products originated from India, against the growth and zearalenone (ZEA) production of Fusarium graminearum. The cell-free supernatants of P. pentosaceus (PPCS) were prepared and chemical profiling was carried out by GC-MS and MALDI-TOF analysis. Chemical profiling of PPCS evidenced that, the presence of phenolic antioxidants, which are responsible for the antifungal activity. Another hand, MALDI-TOF analysis also indicated the presence of antimicrobial peptides. To know the antioxidant potential of PPCS, DPPH free radical scavenging assay was carried out and IC50 value was determined as 32 ± 1.89 μL/mL. The antifungal activity of P. pentosaceus was determined by dual culture overlay technique and zone of inhibition was recorded as 47 ± 2.81%, and antifungal activity of PPCS on F. graminearum was determined by micro-well dilution and scanning electron microscopic techniques. The minimum inhibitory concentration (MIC) of PPCS was determined as 66 ± 2.18 μL/mL in the present study. Also a clear variation in the micromorphology of mycelia treated with MIC value of PPCS compared to untreated control was documented. Further, the mechanism of growth inhibition was revealed by ergosterol analysis and determination of reactive oxygen species (ROS) in PPCS treated samples. The effects of PPCS on mycelial biomass and ZEA production were observed in a dose-dependent manner. The mechanism behind the suppression of ZEA production was studied by reverse transcriptase qPCR analysis of ZEA metabolic pathway genes (PKS4 and PKS13), and results showed that there is a dose dependent down-regulation of target gene expression in PPCS treated samples. The results of the present study were collectively proved that, the antifungal and ZEA inhibitory activity of PPCS against F. graminearum and it may find a potential application in agriculture and food

At least three outbreaks of listeriosis associated with seafood have been reported. Listeria monocytogenes is widely distributed in the general environment including fresh water, coastal water and live fish from these areas. Contamination or recontamination of seafood may also take place during...

Full Text Available AbstractThe objectives of this study were i to isolate Listeria spp. and Listeria monocytogenes in broiler wing meat samples, ii to confirm the isolates by PCR, based on prs and hly A gene sequences, iii to determine the seasonal and monthly distribution of the isolates. A total of 120 broiler wing meat samples (60 packaged pieces wrapped using strech film in styrofoam plates and 60 unpackaged pieces bought from different markets in Hatay province were analysed. Listeria spp. was isolated from 57 (47.5% out of 120 samples. Fifty-four, out of 57 Listeria spp. isolates were identified as L. monocytogenes. L. monocytogenes was isolated from the samples collected during the spring, winter, summer, and autumn at the levels of 26.6%, 40%, 53.3%, 60%, respectively. In this study, the isolation rates were found to be the highest in autumn, while the isolation rates were found to be the lowest in spring. As a consequence, high prevalence of Listeria spp. and L. monocytogenes in poultry wing meat samples may pose a risk for human health. We consider that with obeying the rules of good hygiene practices (GHP, good manufacturing practices (GMP and HACCP can minimize the contamination with Listeria spp.

This AOAC GovVal study compared the VIDAS Listeria monocytogenes II (LMO2) to the Health Products and Food Branch MFHPB-30 reference method for detection of L. monocytogenes in ready-to-eat (RTE) meats. The VIDAS LMO2 test is an automated enzyme-linked fluorescent immunoassay for the detection of L. monocytogenes in foods. The LMO2 test, following the enrichment procedure from the MFLP-33 method, also included use of the chromogenic media, chromID Ottaviani Agosti Agar (OAA) and chromID Lmono for confirmation of LMO2 presumptive results. In previous AOAC validation studies comparing the VIDAS LMO2 method to the U.S. Food and Drug Administration Bacteriological Analytical Manual and U.S. Department of Agriculture-Food Safety and Inspection Service reference methods, LMO2 was approved as AOAC Official Method 2004.02 for the detection of L. monocytogenes in dairy products, vegetables, seafood, raw meats and poultry, and processed meats and poultry. The GovVal comparative study included 20 replicate test portions, each at two contamination levels for each matrix, where fractionally positive results (5-15 positive results/20 replicate portions tested) were obtained by at least one method at one level. Five uncontaminated controls were included. Chi-square analysis of the comparative data in this study indicates no statistical differences between the VIDAS LMO2 and the MFHPB-30 standard methods at the 5% level of significance. Confirmation of presumptive LMO2 results with the chromogenic OAA and Lmono media was shown to be equivalent to the appropriate reference method agars. The data demonstrate that the VIDAS LMO2 method is an acceptable alternative method to the MFHPB-30 standard culture method for the detection of L. monocytogenes in RTE meats, including liver paté, hot dogs, raw fermented sausage, sliced deli turkey, and sliced deli ham.

Full Text Available Challenge tests are the preferable methodology to study the behaviour of Listeria monocytogenes on ready to eat foods, according to Regulation (EC 2073/2005. Challenge testing using L. monocytogenes in seasoned salami from different food business operators showed, after seasoning of the product, a count reduction of the inoculated organisms without any further growth of the pathogen; however differences of L. monocytogenes behaviour could be observed according to different production protocols.

Full Text Available In the EU, food is considered safe with regard to Listeria monocytogenes if its numbers do not exceed 100 CFU/g throughout the shelf-life of the food. Therefore, it is important to determine if a food supports growth of L. monocytogenes. Challenge studies to determine the ability of a food to support growth of L. monocytogenes are essential as predictive modelling often overestimates the growth ability of L. monocytogenes. The aim of this study was to determine if growth of L. monocytogenes was supported during the production and distribution of mushrooms. A three-strain mixture of L. monocytogenes was inoculated onto three independent batches of whole mushrooms, sliced mushrooms, mushroom casing and mushroom substrate at a concentration of about 100–1000 CFU/g. The batches were incubated at potential abuse temperatures, as a worst case scenario, and at intervals during storage L. monocytogenes numbers, % moisture and pH were determined. The results showed that the sliced and whole mushrooms had the ability to support growth, while mushroom casing allowed survival but did not support growth. Mushroom substrate showed a rich background microflora that grew on Listeria selective media and this hindered enumeration of L. monocytogenes. In the case of this study, Combase predictions were not always accurate, indicating that challenge studies may be a necessary part of growth determination of L. monocytogenes.

This study examined the effects of three lactic acid bacteria (LAB) strains on the nematode Caenorhabditis elegans. Lactobacillus salivarius, Lactobacillus reuteri, and Pediococcus acidilactici were found to inhibit the development and growth of the worm. Compared to Escherichia coli used as the control, L. reuteri and P. acidilactici reduced the lifespan of wild-type and short-lived daf-16 worms. On the contrary, L. salivarius extended the lifespan of daf-16 worms when used live, but reduced it as UV-killed bacteria. The three LAB induced the expression of genes involved in pathogen response and inhibited the growth of tumor-like germ cells, without affecting DAF16 localization or increasing corpse cells. Our results suggest the possible use of C. elegans as a model for studying the antitumor attributes of LAB. The negative effects of these LAB strains on the nematode also indicate their potential use against parasitic nematodes.

Thirty-two agar sausage models were arranged in a 2((5-1)) fractional factorial design to analyse the effects of Penicillium nalgio-vense growth, Pediococcus pentosaceus starter, sodium ascorbate, sodium nitrate and temperature on 79 volatiles produced during incubation. The model focused...... on the outer 10 millimeters of sausages. Ascorbate addition showed clear antioxidative effects, and reduced the amount of more than half of all volatiles but increased concentrations of 2-methyl-propanal and 3-methyl-butanal. The effects of P. pentosaceus and Micrococcaceae were confounded, but together...... they had pronounced antioxidative effects, lowering the amount of straight chain aldehydes, 2-alkenals, furanes and ketones. P. pentosaceus and Micrococcaceae growth increased the leucine catabolites 3-methyl-butanal and 3-methyl-1-butanol. P. nalgiovense decreased the concentrations of 2-heptanone, 2...

We present a case of colovesical fistula presenting with a clinical syndrome of urosepsis subsequently demonstrated to be due to Listeria monocytogenes bacteraemia. The patient had a history of previous rectal cancer with a low anterior resection and a covering ileostomy that had been reversed 6 months prior to this presentation. L. monocytogenes was also isolated among mixed enteric organisms on urine culture. There were no symptoms or signs of acute gastrointestinal listeriosis or meningoencephalitis. This unusual scenario prompted concern regarding the possibility of communication between bowel and bladder, which was subsequently confirmed with CT and a contrast enema. The patient recovered well with intravenous amoxicillin and to date has declined surgical management of his colovesical fistula. This case illustrates the importance of considering bowel pathology when enteric organisms such as Listeria are isolated from unusual sites.

The use of replication-deficient adenoviruses as vehicles for transfer of foreign genes offers many advantages in a vaccine setting, eliciting strong cellular immune responses involving both CD8(+) and CD4(+) T cells. Further improving the immunogenicity, tethering of the inserted target Ag to MHC...... class II-associated invariant chain (Ii) greatly enhances both the presentation of most target Ags, as well as overall protection against viral infection, such as lymphocytic choriomeningitis virus (LCMV). The present study extends this vaccination concept to include protection against intracellular...... bacteria, using Listeria monocytogenes as a model organism. Protection in C57BL/6 mice against recombinant L. monocytogenes expressing an immunodominant epitope of the LCMV glycoprotein (GP33) was greatly accelerated, augmented, and prolonged following vaccination with an adenoviral vaccine encoding GP...

Monitoring of food and environmental samples for biological threats, such as Listeria monocytogenes, requires probes that specifically bind biological agents and ensure their immediate and efficient detection. There is a need for robust and inexpensive affinity probes as an alternative to antibodies. These probes may be recruited from random peptide libraries displayed on filamentous phage. In this study, we selected from two phage peptide libraries phage clones displaying peptides capable of specific and strong binding to the L. monocytogenes cell surface. The ability of isolated phage clones to interact specifically with L. monocytogenes was demonstrated using enzyme-linked immunosorbent assay (ELISA) and confirmed by co-precipitation assay. We also assessed the sensitivity of phage-bacteria binding by PCR on phage-captured Listeria cells, which could be detected at a concentration of 10{sup 4} cells ml{sup -1}. In addition, as proof-of-concept, we tested the possibility of immobilizing the affinity-selected phages to a putative biosensor surface. The quality of phage deposition was monitored by ELISA and fluorescent microscopy. Phage-bacterial binding was confirmed by high power optical phase contrast microscopy. Overall, the results of this work validate the concept of affinity-selected recombinant filamentous phages as probes for detecting and monitoring bacterial agents under any conditions that warrant their recognition, including in food products.

Monitoring of food and environmental samples for biological threats, such as Listeria monocytogenes, requires probes that specifically bind biological agents and ensure their immediate and efficient detection. There is a need for robust and inexpensive affinity probes as an alternative to antibodies. These probes may be recruited from random peptide libraries displayed on filamentous phage. In this study, we selected from two phage peptide libraries phage clones displaying peptides capable of specific and strong binding to the L. monocytogenes cell surface. The ability of isolated phage clones to interact specifically with L. monocytogenes was demonstrated using enzyme-linked immunosorbent assay (ELISA) and confirmed by co-precipitation assay. We also assessed the sensitivity of phage-bacteria binding by PCR on phage-captured Listeria cells, which could be detected at a concentration of 104 cells ml-1. In addition, as proof-of-concept, we tested the possibility of immobilizing the affinity-selected phages to a putative biosensor surface. The quality of phage deposition was monitored by ELISA and fluorescent microscopy. Phage-bacterial binding was confirmed by high power optical phase contrast microscopy. Overall, the results of this work validate the concept of affinity-selected recombinant filamentous phages as probes for detecting and monitoring bacterial agents under any conditions that warrant their recognition, including in food products.

The Danish regulatory policy on Listeria monocytogenes in foods is based on the principles of HACCP and was developed using a health risk assessment approach. The Danish policy focuses examinations and criteria for L. monocytogenes in ready-to-eat foods and is based on a combination of inspection...

Listeria monocytogenes is notorious for its capacity to colonize the environment and equipment of food processing facilities and to persist in the processing plant ecosystem, sometimes for decades. Such persistence is mediated by multiple attributes of L. monocytogenes, including the pathogen’s capa...

Much progress of application of bacterial vaccine in treatment and prevention of tumor was acquired,which showed broad prospect in clinical study of animals and humans. Listeria monocytogenes( L. monocytogenes) was considered much important by virtue of its special characteristic of biology and immunology.L. monocytogenes was ingested by professional or part-time phagocytes,survived and proliferated in the phagocytes under synergism of toxic factor secreted by itself,meanwhile,the cellular and humoral immune response was induced. Antigenic gene of specific tumor was loaded in the attenuated L. monocytogenes,which can enhance immune response of host cells. Effective cell targeted to enter tumor tissue and acted on tumor cells to induce apoptosis of tumor cells. Tumor degenerated not easy to reappear. Therefore,recombinant attenuated L. monocytogenes was a safe and effective anti-cancer vaccine vector. Now the work of researchers mainly focuses on solving practical problem in clinical application. Biological characteristics of L. monocytogenes,feasibility and superiority of L. monocytogenes as targeted vaccine vector,problem and prospect of L. monocytogenes in clinical application of anti-tumor were reviewed in this paper.

The food-borne pathogen Listeria monocytogenes is a Gram-positive facultative anaerobic rod, which is the causative agent of listeriosis. Due to the severity of the disease and the fact that its incidence is increasing in numerous European countries, L. monocytogenes is of great public health concer

Listeria monocytogenes frequently exhibits resistance to arsenic. We report here the draft genome sequences of eight genetically diverse arsenic-resistant L. monocytogenes strains from human listeriosis and food-associated environments. Availability of these genomes would help to elucidate the role ...

Listeria monocytogenes has been implicated in a number of outbreaks involving fresh produce, including an outbreak in 2016 resulting from contaminated packaged salads. The persistence and internalization potential of L. monocytogenes in romaine lettuce was evaluated, and the persistence of two L. mo...

Pediococci are halophilic lactic acid bacteria, within the family Lactobacillaceae, which are involved in the fermentation of various salted and fermented foods, such as kimchi and jeotgal. In this study, a matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MS method was developed for the rapid identification of species of the genus Pediococcus. Of the 130 Pediococcus spectra aligned with the Biotyper taxonomy database, 122 isolates (93.9 %) yielded log scores genus Pediococcus, all of the isolates were correctly identified, of which 84 (64.6 %) and 46 (35.4 %) were identified at the species and genus level, respectively. In comparing food origins, no relationship was found between the bacterial characteristics and food environment. We were able to produce a Biotyper system for identification of members of the genus Pediococcus with locally extended Pediococcus reference strains. The MALDI-TOF MS method is fast, simple and reliable for discriminating between species in the genus Pediococcus and therefore will be useful for quality control in determining the spoilage of alcoholic beverages or in the production of fermented food.

Three strains of Pediococcus pentosaceus are each intended to improve the ensiling process at a dose of 1x108 CFU/kg fresh matter. This speciesis considered by EFSA to be suitable for the qualified presumption of safety approach to safety assessment. As the identity of the strains has been established and as no resistance to antibiotics of human and veterinary clinical significance was detected, the use of the strains in the production of silage is presumed safe for livestock species, consume...

Full Text Available Probiotics are regarded as panacea for modern life. Aim of the study was to formulate the capsule comprising probiotic strain, Pediococcus spp. GS4 isolated from fermented food, Khadi and to examine its viability with and without excipients by exposing to simulated gastric fluid (SGF and simulated intestinal fluid (SIF at different time intervals. The empty hard gelatin capsule was filled with FDPP [Freeze dried powder of Pediococcus spp. GS4] aseptically adding excipients (lactose, ascorbic acid and inulin as Test and without excipients as Control. For stability studies both Test and Control capsules were stored at 4 ±1ºC for 28 days. In vitro viability of probiotic cells were studied using SGF and SIF respectively. The optimal composition of effective formula was found to be composed of 6% lactose, 2.5% ascorbic acid and 2% inulin which could protect maximum viability of cells. After 28 days, the viability of Test was improved by 3.73 logs (CFU/ml as compared to Control at 4 ±1º C (P < 0.05. Significant difference was observed between Test and Control when incubated sequentially in SGF (pH 2.5; 45 min and 90 min and SIF (pH 6.8; 150 min and 210 min. Hence, in vitro test showed that combination of suitable excipients have significant effect on the survival of Pediococcus spp. GS4 when exposed to gastrointestinal conditions (SGF, SIF.

The synergy inhibition of two lactic acid bacteria strains, Lactobacillus curvatus and Pediococcus acidilactici H,on the growth of Listeria monocytogenes in frozen beef was investigated. A Lactobacillus curvatus strain( producing the bacteriocin sakacin P)and a Pediococcus acidilactici H (producing bacteriocin pediocin AcH)were inoculated alone or together in a Listeria-seeded raw pork meat which was stored at 4℃ for 6 weeks.The growth of Listeria monocytogenes was controlled by adding either LAB strain alone,yet the rebound appeared after one-week storage. However,the time of inhibition was prolonged by adding combined these two LAB strains to 6 weeks, after when the Listeria monocytogenes had a rebound with the cfu count lower than 10cfu · g-1.Therefore, using the combined these two LAB strains can effectively delay the rebound of Listeria monocytogenes in the beef.%研究了弯曲乳酸杆菌和乳酸片球菌对低温冷藏牛肉中李斯特菌的混合协同抑制作用.李斯特菌、弯曲乳酸杆菌(产细菌素sakacin P)和乳酸片球菌(产生片球菌素AcH),单独或混合接种于冷鲜牛肉中,4℃下储藏6周.单一接种弯曲乳酸杆菌或乳酸片球菌均能对李斯特菌起到抑制作用,但一周后均出现李斯特菌再次污染现象;然而混合接种弯曲乳酸杆菌和乳酸片球菌能将对李斯特菌的抑制期延长至第六周,之后才出现反弹现象,且李斯特菌数低于10cfu·g-1.因此,应用组合产细菌素菌株能有效延长对李斯特菌的抑制作用.

Two bacterial isolates with inhibitory activity against Listeria monocytogenes and Enterococcus faecalis were obtained from soil. Genotypic and phenotypic characterization identified them as Enterococcus mundtii, a species whose ability to compete with L. monocytogenes is relatively unexplored compared to other members of the genus. The thermal stability of the inhibitory factor and its sensitivity to proteolytic enzymes indicate that it is most likely a bacteriocin. Both isolates grew at comparable rates to L. monocytogenes at 5 °C and 10 °C in vitro. One isolate killed L. monocytogenes when it reached concentrations of 10(6)-10(8) CFU ml(-1). Minimum inocula of 10(6) and 10(5) CFU ml(-1) of E. mundtii were required to reduce and maintain L. monocytogenes concentrations beneath the level of detection at 5 °C and 10 °C, respectively. In situ experiments at 5 °C showed that E. mundtii inhibited the growth of L. monocytogenes on vacuum-packed cold smoked salmon during its four week shelf life. E. mundtii could, therefore, control the growth of L. monocytogenes at low temperatures, indicating a potential application in controlling this pathogen in chilled foods. To control growth of Listeria, the concentration of E. mundtii needs to be high, but it is possible that a purified bacteriocin could be used to achieve the same effect.

Full Text Available The aim of this experiment was to identify isolates obtained from feces of Indonesian infants and to evaluate their capability as probiotics. Identification of isolates was carried out based on morphology, physiology and biochemical identifications, and molecular identification based on 16S rRNA sequence. Morphological and physiological identification was carried out based on Gram staining, shape, motility, spore formation and catalase production. Biochemical identifications based on production of CO2 and NH3 from glucose, the ability to grow on different temperature (10 and 45°C and pH (4.4 and 9.6, and different salt concentration (6.5 and 18%. Probiotics capability of isolates was assayed on the ability to grow on low pH (pH 2.0, on different bile salts concentration (0.3; 0.5; 1.0 and 1.5%, the capacity to grow on media with inulin as the only carbon source, and in vitro adhesion ability on porcine mucin. Morphological, physiological and biochemical identification suggest that all of isolates belong to lactic acid bacteria. Further molecular identification of five isolates showedthat isolates AA, BE and BK were strains of Pediococcus acidilactici (similarity 99%, while isolate AP and AG were strains of Lactobacillus casei (similarity 99-100%. Probiotic assays showed that more than 80% of cells of Pediococcus acidilactici isolates AA, BE and BK were viable after grown on pH 2.0 for 90 min, and around 80% of cells from the same isolates were survived on media supplemented with bile salt 1.5% for 2 h. All of isolates had high adhesion capacity as seen by more than 75% of cells attached on pig gastric mucin. Investigationof isolates to grow on inulin showed Pediococcus acidilactici isolate BE was able to consume inulin as the only carbon source. It is concluded that Pediococcus acidilactici isolate BE was a candidate probiotics and subject to further in vivo evaluation using animal models to examine their beneficial health effects.Key word

Biofilms develop successively on devices of milk production without sufficient cleaning and originate from the microbial community of raw milk. The established biofilm matrices enable incorporation of pathogens like Listeria monocytogenes, which can cause a continuous contamination of food processing plants. L. monocytogenes is frequently found in raw milk and non-pasteurized raw milk products and as part of a biofilm community in milk meters and bulk milk tanks. The aim of this study was to analyze whether different L. monocytogenes strains are interacting with the microbial community of raw milk in terms of biofilm formation in the same manner, and to identify at which stage of biofilm formation a selected L. monocytogenes strain settles best. Bacterial community structure and composition of biofilms were analyzed by a cloning and sequencing approach and terminal restriction fragment length polymorphism analysis (T-RFLP) based on the bacterial 16S rRNA gene. The chemical composition of biofilms was analyzed by Fourier transform infrared spectroscopy (FTIR), while settled L. monocytogenes cells were quantified by fluorescence in situ hybridization (FISH). Addition of individual L. monocytogenes strains to raw milk caused significant shifts in the biofilm biomass, in the chemical as well as in the bacterial community composition. Biofilm formation and attachment of L. monocytogenes cells were not serotype but strain specific. However, the added L. monocytogenes strains were not abundant since mainly members of the genera Citrobacter and Lactococcus dominated the bacterial biofilm community. Overall, added L. monocytogenes strains led to a highly competitive interaction with the raw milk community and triggered alterations in biofilm formation.

The intracellular pathogen Listeria monocytogenes represents a promising therapeutic vector for the delivery of DNA, RNA or protein to cancer cells or to prime immune responses against tumour-specific antigens. A number of biological properties make L. monocytogenes a promising platform for development as a vector for either gene therapy or as an anti-cancer vaccine vector. L. monocytogenes is particularly efficient in mediating internalization into host cells. Once inside cells, the bacterium produces specific virulence factors which lyse the vaculolar membrane and allow escape into the cytoplasm. Once in the cytosol, L. monocytogenes is capable of actin-based motility and cell-to-cell spread without an extracellular phase. The cytoplasmic location of L. monocytogenes is significant as this potentiates entry of antigens into the MHC Class I antigen processing pathway leading to priming of specific CD8(+) T cell responses. The cytoplasmic location is also beneficial for the delivery of DNA (bactofection) by L. monocytogenes whilst cell-to-cell spread may facilitate access of the vector to cells throughout the tumour. Several preclinical studies have demonstrated the ability of L. monocytogenes for intracellular gene or protein delivery in vitro and in vivo, and this vector has also displayed safety and efficacy in clinical trial. Here, we review the features of the L. monocytogenes host-pathogen interaction that make this bacterium such an attractive candidate with which to induce appropriate therapeutic responses. We focus primarily upon work that has led to attenuation of the pathogen, demonstrated DNA, RNA or protein delivery to tumour cells as well as research that shows the efficacy of L. monocytogenes as a vector for tumour-specific vaccine delivery.

EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP

2014-03-01

Full Text Available Pediococcus pentosaceus is a technological additive intended to improve the ensiling process at a minimum proposed dose of 1 × 108 colony-forming units (CFU/kg fresh material. The P. pentosaceus strain was found to be resistant to tetracycline by an unidentified mechanism and thus may pose a risk for the spread of genes coding for resistance to an antibiotic of human and veterinary importance. Thus, the additive containing this strain is not considered safe for the target animals and consumers of products from animals fed the treated silage. The additive should be regarded as a skin and eye irritant and a potential skin and respiratory sensitiser, and treated accordingly. Since the P. pentosaceus strain carries an uncharacterised resistance to tetracycline, the FEEDAP Panel cannot conclude on its safety for the environment. A total of four studies with laboratory-scale silos were made using samples of forage of differing water-soluble carbohydrate content. In each case, replicate silos containing treated forage were compared with identical silos containing the same but untreated forage. Although the additive showed a tendency to increase lactic acid production and reduce pH in the ensiled material, overall there was insufficient evidence of a beneficial effect on the preservation of nutrients.

The aim of this study was to investigate the Pediococcus halophilus addition on the chemical quality of terasi ikan (fermented anchovy paste) product. Two levels of bacterial concentration (106 CFU/mL and 109 CFU/mL) were used as a single starter culture for the fermentation process. Changes in chemical characteristics were observed at day 7, 14 and 21. No differences (p > 0.05) in moisture and protein content were found in the analysis of variance within terasi ikan samples. The decrease in reducing sugar and L-lysine HCl during the fermentation was attributed to the formation of Maillard Reaction Products (MRPs) which was manifested in dark brown color of the end products. The interaction between P. halophilus and terasi ikan microbiota as well as their enzymatic activities were considered to affect vitamin B synthesis and degradation of protein into amino acids and amines. These findings facilitate further investigations on using P. halophilus as constituent of mixed culture, instead of as a single culture for terasi industry in order to produce products of well-controlled quality and safety.

Full Text Available The mutant of Pediococcus pentosaceus (SPAm produced earlier by UV-mutagenesis exhibiting higher dextransucrase activity as compared to wild-type was used. The generated mutant SPAm gave 12.2 mg/ml, a 20% higher dextran than wild-type. Response surface methodology was carried out for further enhancement of dextran production. To enhance dextran production by the mutant SPAm, Plackett-Burman Design and a 2² full factorial Central Composite Design was employed. After response optimization, the optimum concentration of sucrose and yeast extract was 5.115% (w/v and 0.635% (w/v, respectively. The experimental values of dextran 36.0 mg/ml at flask level and 35.0 mg/ml at bioreactor level were in good agreement with the predicted value of 40.8 mg/ml. The increase in dextran production by the mutant SPAm using the optimized medium was 3 fold higher as compared to unoptimized medium.

Full Text Available An eight-week experiment was carried out to determine the effects of dietary Pediococcus pentosaceus as probiotic on the body composition and gut microbiota of Siberian sturgeon, Acipenser baerii. A total of 180 fish with mean body weight of 143±0.01g were randomly distributed into 12 200L fiberglass tanks as four treatments with three replicates, including groups fed with diet containing 2×107, 2×108 and 2×109 CFU g-1 of P. pentosaceus and probiotic-free as control group. Body composition of treatment groups was not influenced by P. pentosaceus except for fat and moisture. The bacteria had a significant colonization in the intestine of fish fed with supplemented diet with P. pentosaceus. High level of acid lactic bacterial load was found in the treatment fed with highest amount of the probiotic i.e. 2×109 CFU g-1. The results showed that application of P. pentosaceus has positive effect on the body composition and intestinal microflora of the A. baerii.

Full Text Available BACKGROUND: Certain intestinal microflora are thought to regulate the systemic immune response. Lactic acid bacteria are one of the most studied bacteria in terms of their beneficial effects on health and autoimmune diseases; one of which is Multiple sclerosis (MS which affects the central nervous system. We investigated whether the lactic acid bacterium Pediococcus acidilactici, which comprises human commensal bacteria, has beneficial effects on experimental autoimmune encephalomyelitis (EAE, an animal model of MS. METHODOLOGY/PRINCIPAL FINDINGS: P. acidilactici R037 was orally administered to EAE mice to investigate the effects of R037. R037 treatment suppressed clinical EAE severity as prophylaxis and therapy. The antigen-specific production of inflammatory cytokines was inhibited in R037-treated mice. A significant increase in the number of CD4(+ Interleukin (IL-10-producing cells was observed in the mesenteric lymph nodes (MLNs and spleens isolated from R037-treated naive mice, while no increase was observed in the number of these cells in the lamina propria. Because only a slight increase in the CD4(+Foxp3(+ cells was observed in MLNs, R037 may primarily induce Foxp3(- IL10-producing T regulatory type 1 (Tr1 cells in MLNs, which contribute to the beneficial effect of R037 on EAE. CONCLUSIONS/SIGNIFICANCE: An orally administered single strain of P. acidilactici R037 ameliorates EAE by inducing IL10-producing Tr1 cells. Our findings indicate the therapeutic potential of the oral administration of R037 for treating multiple sclerosis.

The main goal of this study was to develop an improved oral delivery system for Pediococcus pentosaceus OZF, a promising probiotic bacterium, and to assess its viability under simulated gastrointestinal (GI) tract model by comparing the efficiency of microbiological and molecular approaches. Encapsulation was carried out using extrusion method and as a result, encapsulation system including 0.75 % lactulose, 1.8 % sodium alginate, 0.1 M CaCl2, and 5 min gelling time was shown to have a significantly protective effect against pH 2.0 acid stress over 3 h. However, completely loss of viability was exhibited by free OZF cells under similar conditions. To provide an additional barrier for capsules, coating process was investigated using different biopolymers, and the survival rates of free and encapsulated OZF cells upon expose to simulated GI conditions were detected by conventional culture techniques and propidium monoazide-quantitative polymerase chain reaction (PMA-qPCR) method. No significant differences between the biopolymers were detected, except the chitosan which leads totally 85 % protection and extra 25 % improvement in the survival of OZF cells compared to uncoated capsules. In conclusion, our findings indicated that chitosan-coated capsules provided an important protective effect on the viability of OZF cells against the GI system conditions encountered during the transit of food. In addition, this study was found successful in monitoring the viable OZF cells in capsules using PMA-qPCR method.

EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP

2014-03-01

Full Text Available Pediococcus pentosaceus is a technological additive intended to improve the ensiling process at a minimum proposed dose of 1 × 108 colony-forming units (CFU/kg fresh material. The P. pentosaceus strain was found to be resistant to tetracycline by an unidentified mechanism and thus may pose a risk for the spread of genes coding for resistance to an antibiotic of human and veterinary importance. Thus, the additive containing this strain is not considered safe for the target animals and consumers of products from animals fed the treated silage. The additive should be regarded as a skin and eye irritant and a potential skin and respiratory sensitiser, and treated accordingly. Since the P. pentosaceus strain carries an uncharacterised resistance to tetracycline, the FEEDAP Panel cannot conclude on its safety for the environment. A total of seven studies with laboratory-scale silos were made using samples of forage of differing water-soluble carbohydrate content. In each case, replicate silos containing treated forage were compared with identical silos containing the same but untreated forage. The results showed that the additive has the potential to improve the production of silage from easy, moderately difficult and difficult to ensile forage species by reducing the pH and increasing the preservation of dry matter. This was most consistently shown at application rates of 5 × 107 and 1 × 108 CFU/kg forage.

Full Text Available In this study, the effects of magnolia (Magnolia (M. denudata extract fermentation in increasing the extract’s antioxidative and anticancer activities were investigated. Magnolia was fermented by Pediococcus acidilactici KCCM 11614. The total phenolic content was determined by the Folin-Ciocalteu’s method and the antioxidative effects by 1,1-diphenyl-2-picrylhydrazy (DPPH and ferric reducing ability of plasma (FRAP assay. Anticancer activity against cancer and normal cells was determined using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT. Total phenolic content during fermentation increased from 38.1 to 47.0 mg gallic acid equivalent (GAE/g of solid matter. The radical scavenging activity was 91.4% after 72 h fermentation. Fermented magnolia’s antioxidative effect was threefold higher than that of the (non-fermented control. Fermentation (48 h increased anticanceric activity against AGS, LoVo, and MCF-7 cancer cells 1.29- to 1.36-fold compared with that of the control, but did not affect MRC-5 (normal cells, suggesting that fermented magnolia could be used as a natural antioxidative and anticancer agent.

An aqueous two-phase flotation (ATPF) system based on polyethylene glycol (PEG) and sodium citrate (NaNO3C6H5O7·2H2O) was considered for primary recovery of bacteriocin-like inhibitory substance (BLIS) from Pediococcus acidilactici Kp10. The effects of ATPF parameters namely phase composition, tie-line length (TLL), volume ratio between the two phases (VR), amount of crude load (CL), pH, nitrogen gas flow rate (FR) and flotation time (FT) on the performance of recovery were evaluated. BLIS was mainly concentrated into the upper PEG-rich phase in all systems tested so far. The optimum conditions for BLIS purification, which composed of PEG 8000/sodium citrate, were: TLL of 42.6, VR of 0.4, CL of 22% (w/w), pH 7, average FT of 30min and FR of 20mL/min. BLIS was partially purified up to 5.9-fold with a separation efficiency of 99% under this optimal conditions. A maximum yield of BLIS activity of about 70.3% was recovered in the PEG phase. The BLIS from the top phase was successfully recovered with a single band in SDS-gel with molecular weight of about 10-15kDa. ATPF was found to be an effective technique for the recovery of BLIS from the fermentation broth of P. acidilactici Kp10.

The present investigation deals with the optimization of cell growth rate of the candidate probiotic Pediococcus acidilactici in the presence of the specific prebiotic inulin. Three independent variables viz. concentration of inulin, concentration of glucose and pH have been selected for optimization study using response surface methodology. Theoretical analysis indicates that the maximum cell growth rate occurs at pH 7, 20 g/dm(3) concentration of inulin and 20 g/dm(3) concentration of glucose. Validation of these values has been done through a set of programmed experiments. Studies on cell dynamics in the presence of different concentrations of inulin have also been carried out to identify any limitation on the initial inulin concentration. Results clearly indicate that cell growth is enhanced with the increase in inulin concentration. However, there is a critical value of the prebiotic concentration (20 g/dm(3) inulin) beyond which the cell growth is inhibited. A summative type growth model has been proposed to explain the growth behaviour of P. acidilactici in the presence of the dual substrate, i.e. glucose and inulin. While growth on glucose follows Monod model, Haldane-type substrate-inhibited growth model holds good for growth on inulin. Intrinsic kinetic parameters for all the model equations have been determined experimentally.

Full Text Available The EC Regulation 2073/2005 (1 requires that food processors evaluate the capability of ready-to-use (RTE products to support the development of Listeria monocytogenes when their pH and aW values are favourable to the growth of this microorganism. It is renown that the lactic flora plays an important role in many different foods, both from a technological and a food safety standpoint. This study was aimed to observe the behaviour and the potential anti-Listeria effect of some natural lactic flora present in Italian liver patè crostini (chicken heart and liver, anchovies, onions, capers, starch, no added preservatives through the Combase Predictor – Max Growth Rate predictive software. The natural lactic flora of the crostini demonstrated a variable capability to inhibit the growth of Listeria monocytogenes which depends upon : the concentration of the lactic flora at the beginning of the shelf life period and the subsequent lag phase, the possible release of anti-Listeria substances, and the maximum growth rate.

Full Text Available Listeria monocytogenes is a serious foodborne pathogen that can contaminate food during processing and can grow during food shelf-life. New types of safe and effective food contact materials embedding antimicrobial agents, like silver, can play an important role in the food industry. The present work aimed at evaluating the in vitro growth kinetics of different strains of L. monocytogenes in the presence of silver, both in its ionic and nano form. The antimicrobial effect was determined by assaying the number of culturable bacterial cells, which formed colonies after incubation in the presence of silver nanoparticles (AgNPs or silver nitrate (AgNO3. Ionic release experiments were performed in parallel. A different reduction of bacterial viability between silver ionic and nano forms was observed, with a time delayed effect exerted by AgNPs. An association between antimicrobial activity and ions concentration was shown by both silver chemical forms, suggesting the major role of ions in the antimicrobial mode of action.

Full Text Available The activity of a crude preparation of bacteriocin produced by the chicken meat isolate Leuconostoc mesenteroides 11, was evaluated at 8ºC and 15ºC against Listeria monocytogenes. The pathogen was inoculated in a crude preparation of the bacteriocin and its population was enumerated after 0.5 and 10 days. The title of the bacteriocin in the preparation was determined immediately before inoculation and after 10 days of incubation at both temperatures. As a negative control, a non-bacteriocin producing strain, Leuconostoc mesenteroides A13, was used. Bacteriocin of L. mesenteroides 11 partially inhibited L. monocytogenes at 8ºC, but at 15ºC it was unable to prevent growth of the pathogen. Our findings suggest that the use of the semi-purified bacteriocin of L. mesenteroides 11 probably will not be suitable as a single hurdle to prevent L. monocytogenes growth in foods.A atividade de uma preparação bruta de bacteriocina produzida por Leuconostoc mesenteroides 11, isolado de peito de frango, foi avaliada a 8ºC e 15ºC, contra Listeria monocytogenes. O patógeno foi inoculado em uma preparação bruta da bacteriocina e sua população foi enumerada depois de 0,5 e 10 dias de incubação. O título da preparação de bacteriocina foi determinado no tempo 0 e após 10 dias de incubação em ambas as temperaturas. Como controle negativo, foi utilizada uma cepa não produtora de bacteriocina, Leuconostoc mesenteroides A13. A bacteriocina de L. mesenteroides 11 inibiu parcialmente L. monocytogenes a 8ºC, mas a 15ºC a bacteriocina não foi capaz de impedir a multiplicação do patógeno. Nossos resultados sugerem que o uso da bacteriocina semi-purificada de L. mesenteroides 11 provavelmente não será adequada como único obstáculo para impedir a multiplicação de L. monocytogenes em alimentos.

Full Text Available Listeria monocytogenes is a foodborne pathogen able to persist in food industry and is responsible for a severe illness called listeriosis. The ability of L. monocytogenes to persist in environments is due to its capacity to form biofilms that are a sessile community of microorganisms embedded in a self-produced matrix of extracellular polymeric substances (EPS’s. In this review, we summarized recent efforts performed in order to better characterize the polymeric substances that compose the extracellular matrix (ECM of L. monocytogenes biofilms. EPS extraction and analysis led to the identification of polysaccharides, proteins, extracellular DNA, and other molecules within the listerial ECM. All this knowledge will be useful for increasing food protection, suggesting effective strategies for the minimization of persistence of L. monocytogenes in food industry environments.

Aims: This study elucidates the mechanisms by which a nonbacteriocinogenic Carnobacterium piscicola inhibits growth of Listeria monocytogenes. Methods and Results: Listeria monocytogenes was exposed to live cultures of a bacteriocin-negative variant of C. piscicola A9b in co-culture, in a diffusion...... chamber system, and to a cell-free supernatant. Suppression of maximum cell density (0-3.5 log units) of L. monocytogenes was proportional to initial levels of C. pisciola (10(3)-10(7) CFU ml(-1)). Cell-to-cell contact was not required to cause inhibition. The cell-free C. piscicola supernatant caused...... a decrease in L. monocytogenes maximum cell density, which was abolished by glucose addition but not by amino acid, vitamin or mineral addition. The fermentate also gave rise to a longer lag phase and a reduction in growth rate. These effects were independent of glucose and may have been caused by acetate...

Full Text Available Listeria monocytogenes has become one of the major concerns for food safety. Its ability to survive and replicate at low temperature, pH and high salt concentration, makes the bacterium a threat, mostly for RTE products. For these reasons, the present research was aimed at detecting the ability of growth of L. monocytogenes in RTE products retrieved from one deli store. Samples were analysed for L. monocytogenes detection, then inoculated with the pathogen (105cell/ml and stored at refrigeration temperature for the duration of their shelf-life (15-60 days. In all the products L. monocytogenes was not detected before experimental contamination. The challenge test evidenced that experimentally inoculated L. monocytogenes was not able to multiply for the duration of the entire shelf-life. These results indicated that the tested products could be considered as foods which are not able to support the growth of L. monocytogenes, as indicated by E.C. Regulation 2073/05. However, in order to guarantee consumer’s safety, it needs to be emphasized the need of a correct application of the GMPs, required for lowering the risk of initial contamination.

Full Text Available Listeria species are widely distributed in environment and L. monocytogenes are the causal agent of Listeriosis, the disease that can be serious and fatal to human and animals. The objectives of this study were to detect, isolate and identify Listeria monocytogenes from retail broiler chicken ready to eat meat products in restaurants-Khartoum state, Sudan. A total of 250 retail broiler chicken ready to eat meat products were collected from restaurants in Khartoum State, 50 sample from frozen chicken burger, 50 sample from frozen chicken sausages, 50 sample from frozen chicken meat balls (kofta, 50 sample from chicken shawerma and 50 sample from chicken mortedella, Listeria spp. were isolated by the conventional International Organization for Standardization method and L. monocytogenes identified by biochemical test. The results showed that out of total 250 samples, 95 (38% were found to be contaminated with Listeria spp. the isolation rate was as follows: L. monocytogenes (13.6%, L. ivanovi (20.8%, L. grayi (1.6%, L. seeligeri (0.8% and L. welshimeri (1.2%. The results presented in this study indicate the contamination of retail broiler chicken ready to eat meat products with L. monocytogenes. This study reported the occurrence and distribution of L. monocytogenes and other Listeria species in retail meat products (frozen chicken burger, frozen chicken sausages, frozen chicken meat balls (kofta, chicken shawerma and chicken mortedella, purchased from restaurants in Khartoum state Sudan.

Listeria monocytogenes is a ubiquitous bacterium capable of infecting humans, particularly pregnant women and immunocompromised individuals. Although the intracellular invasion and pathogenesis of listeriosis in mammalian tissues has been well studied, little is known about the ecology of L. monocytogenes , and in particular the environmental reservoir for this bacterium has not been identified. This study used short-term co-culture at 15, 22 and 37 degrees C to examine the interaction of L. monocytogenes strains with Acanthamoeba polyphaga ACO12. Survival of L. monocytogenes cells phagocytosed by monolayers of trophozoites was assessed by culture techniques and microscopy. A. polyphaga trophozoites eliminated bacterial cells within a few hours post-phagocytosis, irrespective of the incubation temperature used. Wild-type L. monocytogenes and a phenotypic listeriolysin O mutant were unable to either multiply or survive within trophozoites. By contrast, Salmonella enterica serovar Typhimurium C5 cells used as controls were able to survive and multiply within A. polyphaga trophozoites. The data presented indicate that A. polyphaga ACO12 is unlikely to harbour L. monocytogenes, or act as an environmental reservoir for this bacterium.

Listeria monocytogenes is the causative agent of the food-borne life threatening disease listeriosis. This pathogenic bacterium received much attention in the endeavor of deciphering the cellular mechanisms that underlie the onset of infection and its ability to adapt to the food processing environment. Although information is available on the presence of L. monocytogenes in many environmental niches including soil, water, plants, foodstuff and animals, understanding the ecology of L. monocytogenes in outdoor environments has received less attention. Soil is an environmental niche of pivotal importance in the transmission of this bacterium to plants and animals. Soil composition, microbial communities and macrofauna are extrinsic edaphic factors that direct the fate of L. monocytogenes in the soil environment. Moreover, farming practices may further affect its incidence. The genome of L. monocytogenes presents an extensive repertoire of genes encoding transport proteins and regulators, a characteristic of the genome of ubiquitous bacteria. Postgenomic analyses bring new insights in the process of soil adaptation. In the present paper focussing on soil, we review these extrinsic and intrinsic factors that drive environmental adaptation of L. monocytogenes.

The critical role of sortase A in gram-positive bacterial pathogenicity makes this protein a good potential target for antimicrobial therapy. In this study, we report for the first time the crystal structure of Listeria monocytogenes sortase A and identify the active sites that mediate its transpeptidase activity. We also used a sortase A (SrtA) enzyme activity inhibition assay, simulation, and isothermal titration calorimetry analysis to discover that chalcone, an agent with little anti-L. monocytogenes activity, could significantly inhibit sortase A activity with an IC50 of 28.41 ± 5.34 μM by occupying the active site of SrtA. The addition of chalcone to a co-culture of L. monocytogenes and Caco-2 cells significantly inhibited bacterial entry into the cells and L. monocytogenes-mediated cytotoxicity. Additionally, chalcone treatment decreased the mortality of infected mice, the bacterial burden in target organs, and the pathological damage to L. monocytogenes-infected mice. In conclusion, these findings suggest that chalcone is a promising candidate for the development of treatment against L. monocytogenes infection.

Full Text Available Listeria monocytogenes, a foodborne bacterial pathogen, is comprised of four phylogenetic lineages that vary with regard to their serotypes and distribution among sources. In order to characterize lineage-specific genomic diversity within L. monocytogenes, we sequenced the genomes of eight strains from several lineages and serotypes, and characterized the accessory genome, which was hypothesized to contribute to phenotypic differences across lineages. The eight L. monocytogenes genomes sequenced range in size from 2.85-3.14 Mb, encode 2,822-3,187 genes, and include the first publicly available sequenced representatives of serotypes 1/2c, 3a and 4c. Mapping of the distribution of accessory genes revealed two distinct regions of the L. monocytogenes chromosome: an accessory-rich region in the first 65° adjacent to the origin of replication and a more stable region in the remaining 295°. This pattern of genome organization is distinct from that of related bacteria Staphylococcus aureus and Bacillus cereus. The accessory genome of all lineages is enriched for cell surface-related genes and phosphotransferase systems, and transcriptional regulators, highlighting the selective pressures faced by contemporary strains from their hosts, other microbes, and their environment. Phylogenetic analysis of O-antigen genes and gene clusters predicts that serotype 4 was ancestral in L. monocytogenes and serotype 1/2 associated gene clusters were putatively introduced through horizontal gene transfer in the ancestral population of L. monocytogenes lineage I and II.

Full Text Available Listeria monocytogenes is the causative agent of the food-borne life threatening disease listeriosis. This pathogenic bacterium received much attention in the endeavour of deciphering the cellular mechanisms that underlie the onset of infection and its ability to adapt to the food processing environment. Although information is available on the presence of L. monocytogenes in many environmental niches including soil, water, plants, foodstuff and animals, understanding the ecology of L. monocytogenes in outdoor environments has received less attention. Soil is an environmental niche of pivotal importance in the transmission of this bacterium to plants and animals. Soil composition, microbial communities and macrofauna are extrinsic edaphic factors that direct the fate of L. monocytogenes in the soil environment. Moreover, farming practices may further affect its incidence. The genome of L. monocytogenes presents an extensive repertoire of genes encoding transport proteins and regulators, a characteristic of the genome of ubiquitous bacteria. Postgenomic analyses bring new insights in the process of soil adaptation. In the present paper focussing on soil, we review these extrinsic and intrinsic factors that drive environmental adaptation of L. monocytogenes.

The use of pediocins as food additives or drugs requires a simple and rapid method by which large quantities of homogeneous pediocin are produced at industrial level. Two centrifugation steps required during initial stages of purification i.e. separation of cells from fermentation broth and collection of precipitates after ammonium sulphate precipitation are the major bottlenecks for their large scale purification. In the present work, pediocin production by a new a dairy strain, Pediococcus pentosaceous NCDC 273 (identical to pediocin PA-1 at nucleotide sequence level), was found to be optimum at initial pH of 6.0 and 7.0 of basal MRS supplemented with 20 g/l of glucose or lactose at 20 and 24 h, respectively. Immobilization of cells through entrapment in alginate-xanthan gum gel beads with chitosan coating resulted in negligible cell release during fermentation. Thus, the cell free extract was directly collected through decantation, avoiding the need of centrifugation step at this stage. Subsequent ammonium sulphate precipitation at isoelectric point of pediocin PA-1 (8.85), using magnetic stirrer at high speed (approx. 1200 rpm), resulted in forceful deposition of precipitates on the wall of precipitation beaker allowing their collection using a spatula, avoiding centrifugation step at this stage also. Further purification using cation-exchange chromatography resulted in yield of 134.4% with more than 320 fold purification with the specific activity of 19×10⁵ AU/mg. The collection of single peak of pediocin at 41.9min in RP-HPLC, overlapping with standard pediocin PA-1, resulted in yield of 1.15 μg from 20 μl of sample applied. The overlapping of RP-HPLC peak and SDS-PAGE band corresponding to 4.6 kDa, confirmed the purity and identity of pediocin 273 as pediocin PA-1.

Full Text Available Listeria monocytogenes, a member of the genus Listeria, is widely distributed in agricultural environments, such as soil, manure and water. This organism is a recognized foodborne pathogenic bacterium that causes many diseases, from mild gastroenteritis to severe blood and/or central nervous system infections, as well as abortion in pregnant women. Generally, processed ready-to-eat and cold-stored meat and dairy products are considered high-risk foods for L. monocytogenes infections that cause human illness (listeriosis. However, recently, several listeriosis outbreaks have been linked to fresh produce contamination around the world. Additionally, many studies have detected L. monocytogenes in fresh produce samples and even in some minimally processed vegetables. Thus L. monocytogenes may contaminate fresh produce if present in the growing environment (soil and water. Prevention of biofilm formation is an important control measure to reduce the prevalence and survival of L. monocytogenes in growing environments and on fresh produce. This article specifically focuses on fresh produce–associated listeriosis outbreaks, prevalence in growing environments, contamination levels of fresh produce, and associated fresh produce safety challenges.

Listeria monocytogenes, a member of the genus Listeria, is widely distributed in agricultural environments, such as soil, manure and water. This organism is a recognized foodborne pathogenic bacterium that causes many diseases, from mild gastroenteritis to severe blood and/or central nervous system infections, as well as abortion in pregnant women. Generally, processed ready-to-eat and cold-stored meat and dairy products are considered high-risk foods for L. monocytogenes infections that cause human illness (listeriosis). However, recently, several listeriosis outbreaks have been linked to fresh produce contamination around the world. Additionally, many studies have detected L. monocytogenes in fresh produce samples and even in some minimally processed vegetables. Thus L. monocytogenes may contaminate fresh produce if present in the growing environment (soil and water). Prevention of biofilm formation is an important control measure to reduce the prevalence and survival of L. monocytogenes in growing environments and on fresh produce. This article specifically focuses on fresh produce–associated listeriosis outbreaks, prevalence in growing environments, contamination levels of fresh produce, and associated fresh produce safety challenges. PMID:28282938

Antioxidant defences and induced oxidative stress tissue damage of the blue shrimp Litopenaeus stylirostris, under challenge with Vibrio nigripulchritudo, were investigated for a 72-h period. For this purpose, L. stylirostris were first infected by immersion with pathogenic V. nigripulchritudo strain SFn1 and then antioxidant defences: superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (Gpx), Total antioxidant status (TAS), glutathiones and induced tissue damage (MDA and carbonyl proteins) were determined in the digestive gland at 0, 12, 24, 48 and 72 h post-infection (h.p.i.). In the meantime, TAS was also measured in the blood. Infection level of the shrimps during the challenge was followed by determining V. nigripulchritudo prevalence and load in the haemolymph of the shrimps. Changes in all these parameters during the 72-h.p.i. period were recorded for control shrimps and shrimps previously fed for one month with probiotic Pediococcus acidilactici MA18/5M at 10(7) CFU g(-1) of feed. Our results showed that immersion with V. nigripulchritudo led to maximal infection level in the haemolymph at 24 h.p.i. preceding the mortality peak recorded at 48 h.p.i. Significant decreases in the antioxidant defences were detected from 24 h.p.i. and beyond that time infection leaded to increases in oxidative stress level and tissue damage. Compared to control group, shrimps fed the probiotic diet showed lower infection (20% instead of 45% at 24 h.p.i. in the control group) and mortality (25% instead of 41.7% in the control group) levels. Moreover, infected shrimp fed the probiotic compared to uninfected control shrimps exhibited very similar antioxidant status and oxidative stress level. Compared to the infected control group, shrimps fed the probiotic sustained higher antioxidant defences and lower oxidative stress level. This study shows that bacterial infection leads to oxidative stress in L. stylirostris and highlighted a beneficial effect of P

Full Text Available Objective. To test non-pasteurized goat’s milk from the village of ‘la Garita’, Northern Santander, for Listeria monocytogenes. Material and methods. 90 samples of non-pasteurized goat’s milk were obtained over a 4 month period; pH and temperature of each sample were measured. The INVIMA technique was used to isolate L. monocytogenes; the species was confirmed by PCR. Results. The study showed that eight goat milk providers of the zone neither had refrigeration nor pasteurized the milk. The prevalence of L. monocytogenes was 3%; 15% of the samples had other species of Listeria. The milk obtained from this zone contained the pathogen that may cause listeriosis in children less than 5 years of age, pregnant women, adults and immunologically compromised patients. Conclusions. This study shows the occurrence of this pathogen in goat’s milk and identified areas of risk for those people who drink goat’s milk.

Full Text Available Listeria monocytogenes has been recognized as a food borne pathogen in humans since the 1980s, but we still understand very little about oral transmission of L. monocytogenes or the host factors that determine susceptibility to gastrointestinal infection, due to the lack of an appropriate small animal model of oral listeriosis. Early feeding trials suggested that many animals were highly resistant to oral infection, and the more reproducible intravenous or intraperitoneal routes of inoculation soon came to be favored. There are a fair number of previously published studies using an oral infection route, but the work varies widely in terms of bacterial strain choice, the methods used for oral transmission, and various manipulations used to enhance infectivity. This mini review will summarize the published literature using oral routes of L. monocytogenes infection and will highlight recent technological advances that have made oral infection a more attractive model system.

Environmental sensing by two-component signal transduction systems is likely to play a role for growth and survival of Listeria monocytogenes both during transmission in food products and within a host organism. Two-component systems typically consist of a membrane-associated sensor histidine...... kinase and a gene regulatory protein, the response regulator (RR). We have identified seven putative RR genes in L. monocytogenes LO28 by PCR using degenerate oligonucleotide primers. By insertional inactivation we obtained data suggesting that three of the putative RRs contribute to the pathogenicity...... of L. monocytogenes in mice. Strikingly, the mutants that were attenuated in virulence also had a decreased ability to grow in the presence of various stress conditions potentially encountered in an infection process. Thus, our data point to a connection between the ability of the putative two...

Listeria monocytogenes is a food-borne pathogen that is capable of living in harsh environments. It is believed to do this by forming biofilms, which are surface-associated multicellular structures encased in a self-produced matrix. In this paper we show that in L. monocytogenes extracellular DNA...... (eDNA) may be the only central component of the biofilm matrix and that it is necessary for both initial attachment and early biofilm formation for 41 L. monocytogenes strains that were tested. DNase I treatment resulted in dispersal of biofilms, not only in microtiter tray assays but also in flow...... cell biofilm assays. However, it was also demonstrated that in a culture without eDNA, neither Listeria genomic DNA nor salmon sperm DNA by itself could restore the capacity to adhere. A search for additional necessary components revealed that peptidoglycan (PG), specifically N-acetylglucosamine (NAG...

Following a Listeria monocytogenes detection in a mozzarella cheese sampled at a dairy plant in Lazio Region, further investigations have been conducted both by the competent Authority and the food business operatordairy factory (as a part of dairy factory HACCP control). In total, 90 dairy products, 7 brine and 64 environmental samples have been tested. The prevalence of Listeria monocytogenes was 24.4% in mozzarella cheese, and 9.4% in environmental samples, while brines were all negatives. Forty-seven strains of L. monocytogenes have been isolated, all belonging to 4b/4e serotype. In 12 of these, the macrorestriction profile has been determined by means of pulsed field gel electrophoresis. The profiles obtained with AscI enzyme showed a 100% similarity while those obtained with ApaI a 96.78% similarity. These characteristics of the isolated strains jointly with the production process of mozzarella cheese has allowed to hypothesise an environmental contamination. PMID:27800317

A pastured 2-y-old cross-breed bull developed brainstem encephalitis (rhombencephalitis); Listeria monocytogenes was isolated from the brain. In the brainstem, there was perivascular cuffing, multiple microabscesses, and positive immunostaining for L. monocytogenes. Samples of bovine feces, water, feedstuffs, milking parlor soil, and bulk tank milk were collected from the dairy farm. Seven isolates of the genus Listeria were obtained, 6 of L. innocua and 1 of L. monocytogenes, which was found in the pasture where the bull grazed. Both isolates belonged to serotype 4b and were positive for internalins A, C, and J. According to the DNA fragment patterns of pulsed-field gel electrophoresis, the isolates were closely related. The source of infection was the pasture, implying that listeriosis should not be discounted in cases with compatible clinical signs but the absence of silage feeding.

Listeria monocytogenes is included in the foodborne pathogen, which has been associated with severaloutbreaks of human listeriosis especially in high risk groups. Listeria monocytogenes could be found inGouda cheeses because of poor hygienic and sanitation practices. In addition, this bacteria could surviveduring the making of cheese and cheese ripening process. The purpose of this study was to identify thepresence of L. monocytogenes in local and imported Gouda cheeses and how the safety lev...

The bacteriocin pediocin PA-1 operon of Pediococcus acidilactici PAC1.0 encompasses four genes: pedA, pedB, pedC and pedD. Transcription of the operon results in the formation of two overlapping transcripts, probably originating from a single promoter upstream of pedA. The major transcript comprises

Mechanisms of tetracycline resistance were investigated in two recent Listeria monocytogenes isolates from food, with L. innocua 52P tet(r) as a control. Tetracycline resistance was transferred conjugatively from all three strains to L. ivanovii and from one isolate and the control to Enterococcus faecalis. Molecular analysis demonstrated a chromosomal location for the tet determinant, which was identified as tetM in all cases. These studies are the first to show that L. monocytogenes from food could be a source of tetracycline resistance genes able to spread to other micro-organisms.

A total of 245 strains of Listeria monocytogenes, representing 33 different electrophoretic types (ETs), were examined quantitatively for haemolytic activity. No significant difference was observed in the mean haemolytic activity between different ETs. Eighty four out of 91 strains examined were...... compared with 3.64 among food isolates). The explanation for this may be that more virulent strains are more prone to cause human infection. It is, however, also possible that strains oft. monocytogenes may become more virulent while multiplying in a living organism compared with multiplying in foods....

Environmental sensing by two-component signal transduction systems is likely to play a role for growth and survival of Listeria monocytogenes both during transmission in food products and within a host organism. Two-component systems typically consist of a membrane-associated sensor histidine...... of L. monocytogenes in mice. Strikingly, the mutants that were attenuated in virulence also had a decreased ability to grow in the presence of various stress conditions potentially encountered in an infection process. Thus, our data point to a connection between the ability of the putative two-component...

Listeria monocytogenes cells may induce alkali stress adaptation when exposed to sublethal concentrations of alkaline cleaners and sanitizers that may be frequently used in the food processing environment. In the present study, the effect of temperature on the induction and the stability of such alk...

The objective of this study was to investigate the growth kinetics of Listeria monocytogenes in unsalted and salted (3%) salmon roe. Growth curves, developed using inoculated samples incubated at constant temperatures between 5 and 30 degrees C, were analyzed by curve-fitting to the Huang and Baran...

Full Text Available In recent years in the countries of the European Union have occurred profound and radical changes regarding the safety and hygiene of foodstuffs. The aim of this work is to highlight the significant changes made by the recent legislation in the control of Listeria monocytogenes.

Humans are frequently exposed to Listeria monocytogenes, and high numbers may be ingested during consumption of certain types of food. However, epidemiological investigations show that listeriosis is a rare disease. Risk assessment studies using an animal mouse model indicate that almost all L. mono

Listeria monocytogenes is an important food-borne pathogen that may cause severe infections in humans. Many outbreaks caused by this organism have been associated with ready-to-eat foods wich may have undergone some form of minimal processing, or have been contaminated after processing. Ready-to-eat

Between 1993 and 2003, three infants, two girls and a boy, were found to have an invasive infection with Listeria monocytogenes. They received intensive care including respiratory and circulatory support, antibiotics, and treatment of the neurological complications when possible. One of the girls

Listeria monocytogenes is a ubiquitous, saprophytic, Gram-positive bacterium and occasional food-borne pathogen, often associated with ready-to-eat meat products. Because of the increased consumer interest in organic, all natural, and free range poultry products, it is important to understand L. monocytogenes in the context of such systems. Pasture-reared poultry were surveyed over the course of two 8-wk rearing periods. Cecal, soil, and grass samples were collected for Listeria isolation and characterization. Seven of 399 cecal samples (or 1.75%) were Listeria-positive. All positive cecal samples were obtained from broilers sampled at 2 wk of age. Grass and soil samples were collected from the pasture both before and after introduction of the poultry. Environmental samples collected after introduction of poultry were significantly more likely to contain Listeria (P Listeria, sigB allelic typing, and hlyA PCR tests found that both L. monocytogenes and L. innocua, including hemolytic L. innocua, were recovered from the cecal and environmental (grass/soil) samples. The sigB allelic typing also revealed that (1) positive samples could be composed of 2 or more allelic types; (2) allelic types found in cecal samples could also be found in the environment; and (3) allelic types could persist through the 2 rearing periods. Our data indicate that both pasture-reared poultry and their environment can be contaminated with L. monocytogenes and hemolytic L. innocua.

Full Text Available Objective: To investigate the presence of Listeria monocytogenes in the silage samples. Methods: Silage samples obtained from 150 different farms in Shahrekord city (Iran and after DNA extraction, all samples were analyzed by PCR technique using one pair of primers for presence of this pathogen. The amplified products were detected on 1.5% agarose gel electrophoresis. Results: Listeria monocytogenes was isolated in 4 (2% of the 150 samples. The detection of this bacterium from silage samples in Shahrekord city indicated that these products could create a serious risk in public health of animal and human. The findings showed that in positive silage samples for Listeria monocytogenes, the pH value was about five and it was due to bacterial activity in these products. Conclusions: The quality of silage and hygiene parameters and good herd health management play an important role in the microbiological quality of herd and farm. Considering the high specificity and sensitivity of the employed PCR technique, it is recommended to be useful technique for identification of Listeria monocytogenes.

Animal Production Research Advances ... New food borne infectious diseases have continued to emerge world over in the food industries. ... Its' public health importance cannot be over emphasized as L. monocytogenes causes huge economic ... It is therefore, suggested that proper control strategies, good quality control ...

Prediction of microbial growth kinetics can differ from the actual behavior of the target microorganisms. In the present study, the impact of strain variability on maximum specific growth rate (µmax) (h- 1) was quantified using twenty Listeria monocytogenes strains. The µmax was determined as functi

More than 98% of reported human listeriosis cases are caused by Listeria monocytogenes serotypes within lineages I and II. Serotypes within lineage III (4a and 4c) are commonly isolated from environmental and food specimens. We report the first complete genome sequence of a lineage III isolate, HCC2...

Fatty acids and monoglycerides were evaluated in brain heart infusion broth and in milk for antimicrobial activity against the Scott A strain of Listeria monocytogenes. C12:0, C18:3, and glyceryl monolaurate (monolaurin) had the strongest activity in brain heart infusion broth and were bactericidal at 10 to 20 micrograms/ml, whereas potassium (K)-conjugated linoleic acids and C18:2 were bactericidal at 50 to 200 micrograms/ml. C14:0, C16:0, C18:0, C18:1, glyceryl monomyristate, and glyceryl monopalmitate were not inhibitory at 200 micrograms/ml. The bactericidal activity in brain heart infusion broth was higher at pH 5 than at pH 6. In whole milk and skim milk, K-conjugated linoleic acid was bacteriostatic and prolonged the lag phase especially at 4 degrees C. Monolaurin inactivated L. monocytogenes in skim milk at 4 degrees C, but was less inhibitory at 23 degrees C. Monolaurin did not inhibit L. monocytogenes in whole milk because of the higher fat content. Other fatty acids tested were not effective in whole or skim milk. Our results suggest that K-conjugated linoleic acids or monolaurin could be used as an inhibitory agent against L. monocytogenes in dairy foods.

Listeria monocytogenes is an important foodborne pathogen commonly isolated from food processing environments and food products. This organism can multiply at refrigeration temperatures, form biofilms on different materials and under various conditions, resist a range of environmental stresses, and contaminate food products by cross-contamination. L. monocytogenes is recognized as the causative agent of listeriosis, a serious disease that affects mainly individuals from high-risk groups, such as pregnant women, newborns, the elderly, and immunocompromised individuals. Listeriosis can be considered a disease that has emerged along with changing eating habits and large-scale industrial food processing. This disease causes losses of billions of dollars every year with recalls of contaminated foods and patient medical treatment expenses. In addition to the immune status of the host and the infecting dose, the virulence potential of each strain is crucial for the development of disease symptoms. While many isolates are naturally virulent, other isolates are avirulent and unable to cause disease; this may vary according to the presence of molecular determinants associated with virulence. In the last decade, the characterization of genetic profiles through the use of molecular methods has helped track and demonstrate the genetic diversity among L. monocytogenes isolates obtained from various sources. The purposes of this review were to summarize the main methods used for isolation, identification, and typing of L. monocytogenes and also describe its most relevant virulence characteristics.

Listeria monocytogenes is an important food-borne pathogen that may cause severe infections in humans. Many outbreaks caused by this organism have been associated with ready-to-eat foods wich may have undergone some form of minimal processing, or have been contaminated after processing. Ready-to-eat

Listeria monocytogenes cells may induce alkali stress adaptation when exposed to sublethal concentrations of alkaline cleaners and sanitizers that may be frequently used in the food processing environment. In the present study, the effect of temperature on the induction and the stability of such alk...

Humans are frequently exposed to Listeria monocytogenes, and high numbers may be ingested during consumption of certain types of food. However, epidemiological investigations show that listeriosis is a rare disease. Risk assessment studies using an animal mouse model indicate that almost all L.

Probiotic lactic acid bacteria are being proposed to cure peptic ulcers by reducing colonization of Helicobacter pylori within the stomach mucosa and by eradicating already established infection. In lieu of that, in vitro inhibitory activity of pediocin-producing probiotic Pediococcus acidilactici BA28 was evaluated against H. pylori by growth inhibition assays. Further, chronic gastritis was first induced in two groups of C57BL/6 mice by orogastric inoculation with H. pylori with polyethylene catheter, and probiotic P. acidilactici BA28 was orally administered to study the eradication and cure of peptic ulcer disease. H. pylori and P. acidilactici BA28 were detected in gastric biopsy and fecal samples of mice, respectively. A probiotic treatment with P. acidilactici BA28, which is able to eliminate H. pylori infection and could reverse peptic ulcer disease, is being suggested as a co-adjustment with conventional antibiotic treatment. The study provided an evidence of controlling peptic ulcer disease, by diet mod

A 56-day feeding trial was conducted on a species of ornamental fish called green terror (Aequidens rivulatus) (0.388 ± 0.0021 g) to assess the effect of probiotic bacteria, Pediococcus acidilactici on the growth indices and innate immune response. The fish were randomly allocated into 9 oval tanks (120 l) at a density of 60 fish per tank. The experimental diets were comprised of the control (C), C complemented with fish oil (O) and the probiotic and fish oil (PA) and fed ad lib twice a day. The growth indices (specific growth rate (SGR), feed conversion ratio (FCR) and immunological indices of fish fed the diets including lysozyme activity, total immunoglobulin and alternative complement activity were measured. The Fish fed with the diet containing P. acidilactici (PA) displayed significantly (P terror.

Exopolysaccharide production by lactic acid bacteria is beneficial in the dairy and oat-based food industries and is used to improve the texture of the fermented products. However, beta-D-glucan-producing bacteria are considered spoilage microorganisms in alcoholic beverages because their secreted exopolysaccharides alter the viscosity of cider, wine, and beer, rendering them unpalatable. The plasmidic glycosyltransferase (gtf) gene of the Pediococcus parvulus 2.6 strain isolated from ropy cider has been cloned and sequenced, and its GTF product was functionally expressed in Streptococcus pneumoniae. The GTF protein, which has glycosyltransferase activity, belongs to the COG1215 membrane-bound glycosyltransferase family, and agglutination tests revealed that the enzyme enables S. pneumoniae to synthesize beta-D-glucan. PCR amplification and Southern blot hybridization showed that the gtf gene is also present at different genomic locations in the beta-D-glucan producers Lactobacillus diolivorans G77 and Oenococcus oeni I4 strains, also isolated from ropy cider. A PCR assay has been developed for the detection of exopolysaccharide-producing bacteria. Forward and reverse primers, included respectively in the coding sequences of the putative glycosyltransferase domain and the fifth trans-membrane segment of the GTF, were designed. Analysis of 76 ropy and nonropy lactic acid bacteria validated the method for specific detection of beta-D-glucan homopolysaccharide producer Pediococcus, Lactobacillus, and Oenococcus strains. The limit of the assay in cider was 3 X 10(2) CFU/ml. This molecular method can be useful for the detection of ropy bacteria in cider before spoilage occurs, as well as for isolation of new exopolysaccharide-producing strains of industrial interest.

Full Text Available In this study, the infl uence of lactic acid fermentation on the quality of tomato powder was evaluated. The eff ect of adding fermented tomato powder to ready-to-cook minced pork meat to improve its nutritional value and sensory characteristics was also analysed. The cell growth of Lactobacillus sakei (7.53 log CFU/g was more intense in the medium containing tomato powder, compared to the growth of Pediococcus pentosaceus (6.35 log CFU/g during 24 h of fermentation; however, higher acidity (pH=4.1 was observed in the tomato powder samples fermented with Pediococcus pentosaceus. The spontaneous fermentation of tomato powder reduced cell growth by 38 % and pH values slightly increased to 4.17, compared to the fermentation with pure LAB. The lactofermentation of tomato powder increased the average β-carotene and lycopene mass fractions by 43.9 and 50.2 %, respectively, compared with the nonfermented samples. Lycopene and β-carotene contents in the ready-to-cook minced pork meat were proportional to the added tomato powder (10 and 30 %. Aft er cooking, β-carotene and lycopene contents decreased, on average, by 24.2 and 41.2 %, respectively. The highest loss (up to 49.2 % of carotenoids was found in samples with 30 % nonfermented tomato powder. Tomato powder fermented with 10 % Lactobacillus sakei KTU05-6 can be recommended as both a colouring agent and a source of lycopene in the preparation of ready-to-cook minced pork meat.

Queso fresco, is a Hispanic non-fermented cheese highly susceptible to contamination with L. monocytogenes. This research was aimed to determine the effect of GRAS antimicrobial ingredients to control L. monocytogenes. Antimicrobials included caprylic acid (CA), Nisaplin(®) (N, 2.5% nisin), a mixture of sodium lactate and sodium diacetate (SL/SD), Lactococcus lactis sbp. lactis DPC 3147, monolaurin, and lactic acid (LA). Batches of queso fresco curds were inoculated with 10(4) CFU/g and stored at 4 °C for three weeks. During storage the count of L. monocytogenes reached 7 to 8 Log CFU/g in control samples. Most individual antimicrobial treatments resulted in less than 1 Log CFU/g reductions in final counts, with the exception of N (0.5 g/kg) and CA (2.9 g/kg) that caused more than 3 and 5 Log CFU/g differences with controls, respectively. Mixtures of ingredients were more effective in inhibiting L. monocytogenes growth, and treatments with N and CA consistently delivered 6 Log CFU/g less counts than controls. Supplementation of 12 g/kg LA to treatments with SL/SD (3%/0.22%) caused differences of more than 4 Log CFU/g in final Listeria populations. Samples treated with the binary mixtures of N and CA (0.5 and 0.7 g/kg, respectively) were evaluated in a consumer panel (n = 67). Panelists slightly preferred control and commercial over treated samples, but all samples were in average rated between "slightly liking" and "moderately liking." These experiments indicated that combined use of antimicrobial ingredients may be an effective way to control the population of Listeria monocytogenes in queso fresco.

This study aimed to update and create a data set from laying hens and broilers regarding contamination by Listeria monocytogenes. Two hundred laying-hen flocks were sampled, with 88 flocks reared in cages and 112 reared on the floor. One hundred forty-five broiler flocks were sampled, with 85 conventional and 60 free-range flocks. A total of 774 and 725 samples were analyzed from laying hens and broilers, respectively. L. monocytogenes was detected in 31 of 200 flocks, yielding an estimated prevalence of 15.5% in laying-hen flocks. Among positive flocks, there appeared a significant (P = 0.004) difference between caged and floor-reared hens, with a higher detection in dust samples from floor-reared hens. In positive caged hen flocks, significant (P = 0.028) differences between dust and fecal samples appeared, with a higher detection in feces than in dust samples. In broiler flocks, L. monocytogenes was isolated in 46 of 145 flocks, yielding an estimated prevalence of 32% (28% in conventional flocks versus 37% in the free-range flocks). L. monocytogenes was isolated in samples taken from conventional flocks with a lower frequency than in free-range flocks (13 versus 18%, respectively). The serotyping of L. monocytogenes strains showed that the majority belonged to type 1/2a in laying-hen flocks (74.3%) and in broiler flocks (40.5%). A significant difference (P = 0.007) between laying hens and broilers was shown for serogroup 4 and for serovar 1/2b (P = 0.007); these serogroups were more prevalent in broilers (40%) than in laying hens (5.7%).

Work was conducted to validate performance of the ANSR(®) for Listeria monocytogenes method in selected food and environmental matrixes. This DNA-based assay involves amplification of nucleic acid via an isothermal reaction based on nicking enzyme amplification technology. Following single-step sample enrichment for 16-24 h for most matrixes, the assay is completed in 40 min using only simple instrumentation. When 50 distinct strains of L. monocytogenes were tested for inclusivity, 48 produced positive results, the exceptions being two strains confirmed by PCR to lack the assay target gene. Forty-seven nontarget strains (30 species), including multiple non-monocytogenes Listeria species as well as non-Listeria, Gram-positive bacteria, were tested, and all generated negative ANSR assay results. Performance of the ANSR method was compared with that of the U.S. Department of Agriculture, Food Safety and Inspection Service Microbiology Laboratory Guidebook reference culture procedure for detection of L. monocytogenes in hot dogs, pasteurized liquid egg, and sponge samples taken from an inoculated stainless steel surface. In addition, ANSR performance was measured against the U.S. Food and Drug Administration Bacteriological Analytical Manual reference method for detection of L. monocytogenes in Mexican-style cheese, cantaloupe, sprout irrigation water, and guacamole. With the single exception of pasteurized liquid egg at 16 h, ANSR method performance as quantified by the number of positives obtained was not statistically different from that of the reference methods. Robustness trials demonstrated that deliberate introduction of small deviations to the normal assay parameters did not affect ANSR method performance. Results of accelerated stability testing conducted using two manufactured lots of reagents predicts stability at the specified storage temperature of 4°C of more than 1 year.

Listeria monocytogenes is a food-borne pathogen capable of forming biofilms and persisting in food processing environments for extended periods of time, thereby potentially contaminating foods. The efficacy of octenidine hydrochloride (OH) for inactivating planktonic cells and preformed biofilms of L. monocytogenes was investigated at 37, 21, 8, and 4 degrees C in the presence and absence of organic matter (rehydrated nonfat dry milk). OH rapidly killed planktonic cells and biofilms of L. monocytogenes at all four temperatures. Moreover, OH was equally effective in killing L. monocytogenes biofilms on polystyrene and stainless steel matrices in the presence and absence of organic matter. The results underscore OH's ability to prevent establishment of L. monocytogenes biofilms by rapidly killing planktonic cells and to eliminate preformed biofilms, thus suggesting that it could be used as a disinfectant to prevent L. monocytogenes from persisting in food processing environments.

Background and Purpose Encephalitis caused by Listeria monocytogenes (L. monocytogenes) is rare but sometimes fatal. Early diagnosis is difficult using routine cerebrospinal fluid (CSF) tests, while next-generation sequencing (NGS) is increasingly being used for the detection and characterization of pathogens. Methods This study set up and applied unbiased NGS to detect L. monocytogenes in CSF collected from three cases of clinically suspected listeria meningoencephalitis. Results Three cases of patients with acute/subacute meningoencephalitis are reported. Magnetic resonance imaging and blood cultures led to a suspected diagnosis of L. monocytogenes, while the CSF cultures were negative. Unbiased NGS of CSF identified and sequenced reads corresponding to L. monocytogenes in all three cases. Conclusions This is the first report highlighting the feasibility of applying NGS of CSF as a diagnostic method for central nervous system (CNS) L. monocytogenes infection. Routine application of this technology in clinical microbiology will significantly improve diagnostic methods for CNS infectious diseases.

The aim of this study was to analyze the changing patterns of Listeria monocytogenes contamination in a cheese processing facility manufacturing a wide range of ready-to-eat products. Characterization of L. monocytogenes isolates included genotyping by pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST). Disinfectant-susceptibility tests and the assessment of L. monocytogenes survival in fresh cheese were also conducted. During the sampling period between 2010 and 2013, a total of 1284 environmental samples were investigated. Overall occurrence rates of Listeria spp. and L. monocytogenes were 21.9% and 19.5%, respectively. Identical L. monocytogenes genotypes were found in the food processing environment (FPE), raw materials and in products. Interventions after the sampling events changed contamination scenarios substantially. The high diversity of globally, widely distributed L. monocytogenes genotypes was reduced by identifying the major sources of contamination. Although susceptible to a broad range of disinfectants and cleaners, one dominant L. monocytogenes sequence type (ST) 5 could not be eradicated from drains and floors. Significantly, intense humidity and steam could be observed in all rooms and water residues were visible on floors due to increased cleaning strategies. This could explain the high L. monocytogenes contamination of the FPE (drains, shoes and floors) throughout the study (15.8%). The outcome of a challenge experiment in fresh cheese showed that L. monocytogenes could survive after 14days of storage at insufficient cooling temperatures (8 and 16°C). All efforts to reduce L. monocytogenes environmental contamination eventually led to a transition from dynamic to stable contamination scenarios. Consequently, implementation of systematic environmental monitoring via in-house systems should either aim for total avoidance of FPE colonization, or emphasize a first reduction of L. monocytogenes to sites where

Recombinant Listeria monocytogenes has many attractive characteristics as a vaccine vector against human immunodeficiency virus (HIV). Wild-type and attenuated Listeria strains expressing HIV Gag have been shown to induce long-lived mucosal and systemic T-cell responses in mice. Using the feline immunodeficiency virus (FIV) model of HIV we evaluated recombinant L. monocytogenes in a challenge system. Five cats were immunized with recombinant L. monocytogenes that expresses the FIV Gag and del...

Full Text Available Abstract Background The bacterium Listeria monocytogenes is a saprotroph as well as an opportunistic human foodborne pathogen, which has previously been shown to consist of at least two widespread lineages (termed lineages I and II and an uncommon lineage (lineage III. While some L. monocytogenes strains show evidence for considerable diversification by homologous recombination, our understanding of the contribution of recombination to L. monocytogenes evolution is still limited. We therefore used STRUCTURE and ClonalFrame, two programs that model the effect of recombination, to make inferences about the population structure and different aspects of the recombination process in L. monocytogenes. Analyses were performed using sequences for seven loci (including the house-keeping genes gap, prs, purM and ribC, the stress response gene sigB, and the virulence genes actA and inlA for 195 L. monocytogenes isolates. Results Sequence analyses with ClonalFrame and the Sawyer's test showed that recombination is more prevalent in lineage II than lineage I and is most frequent in two house-keeping genes (ribC and purM and the two virulence genes (actA and inlA. The relative occurrence of recombination versus point mutation is about six times higher in lineage II than in lineage I, which causes a higher genetic variability in lineage II. Unlike lineage I, lineage II represents a genetically heterogeneous population with a relatively high proportion (30% average of genetic material imported from external sources. Phylograms, constructed with correcting for recombination, as well as Tajima's D data suggest that both lineages I and II have suffered a population bottleneck. Conclusion Our study shows that evolutionary lineages within a single bacterial species can differ considerably in the relative contributions of recombination to genetic diversification. Accounting for recombination in phylogenetic studies is critical, and new evolutionary models that

Full Text Available The occurrence of Listeria monocytogenes in Brazilian ice cream and in some soft and semi-soft cheeses produced and sold in the State of Paraná, Brazil was evaluated. Ninety samples of cheese and sixty samples of ice creams were analyzed following the guidelines outlined by the official institutes, AOAC and FDA. In the ice cream samples no isolation of Listeria spp. was found. The percentage of these ninety samples of cheeses positive for Listeria spp. was 12.20%. Listeria monocytogenes was detected in six (6.70% of the same samples. The presence of Listeria innocua was five (5.50% in the samples analyzed was also observed. According to the results of the work it is possible to presume that there is a potential health risk to the brazilian population, heightened by aging and the increase in immunodepressed. These results indicate the need for the implementation of monitoring of these microorganisms as much by producers as by health inspectors. The results also show that the VIP (visual immunoprecipitation assay is a viable triage method of contaminated samples for the liberation of products for commercialization, as it is quick, reliable and does not require additional equipment other than that normally found in production labs, while presenting reliable results.A ocorrência de Listeria monocytogenes em sorvetes e alguns tipos de queijos macios e semi-macios produzidos e vendidos no Estado do Paraná Brasil foram avaliados. Noventa amostras de queijo e sessenta amostras de sorvete foram analisadas seguindo os protocolos da AOAC e FDA. Nas amostras de sorvete, não ocorreu o isolamento de Listeria spp. Foi detectada Listeria spp em 12,20% de amostras de queijo, das quais 6 (6,70% foram positivas para Listeria monocytogenes. Foi também observada a presença de Listeria innocua em 5 amostras (5,50% das mesmas amostras. Pelos resultados deste trabalho pode-se pressupor que existe um risco potencial à saúde da população brasileira com o

Activation of the Nlrc4 inflammasome results in the secretion of IL-1β and IL-18 through caspase-1 and induction of pyroptosis. L. monocytogenes engineered to activate Nlrc4 by expression of Legionella pneumophilia flagellin (L. monocytogenes L.p.FlaA) are less immunogenic for CD8+ T cell responses than wt L. monocytogenes. It is also known that IL-1β orchestrates recruitment of myelomonocytic cells (MMC), which have been shown to interfere with T cell-dendritic cells (DC) interactions in splenic white pulp (WP), limiting T cell priming and protective immunity. We have further analyzed the role of MMCs in the immunogenicity of L. monocytogenes L.p.FlaA. We confirmed that MMCs infiltrate the WP between 24–48 hours in response to wt L. monocytogenes infection and that depletion of MMCs enhances CD8+ T cell priming and protective memory. L. monocytogenes L.p.FlaA elicited accelerated recruitment of MMCs into the WP. While MMCs contribute to control of L. monocytogenes L.p.FlaA, MMC depletion did not increase immunogenicity of L.p.FlaA expressing strains. There was a significant decrease in L. monocytogenes L.p.FlaA in CD8α+ DCs independent of MMCs. These findings suggest that limiting inflammasome activation is important for bacterial accumulation in CD8α+ DCs, which are known to be critical for T cell response to L. monocytogenes. PMID:24349458

This paper shortly summarizes data related to risk assessment of Listeria monocytogenes. From available data on risk assessment, it is concluded that the levels of L. monocytogenes consumed is an important factor affecting the incidence of listeriosis. Foods that do not support the growth of L....... monocytogenes are unlikely to be a source of listeriosis, whereas foods that support the growth to high levels, should be the target of risk management efforts. Based on current epidemiological information from several countries, a concentration of L. monocytogenes not exceeding 100/g of food at the time...

Full Text Available The morphological, physiological and epidemiological features of L. monocytogenes, together with the severity of human listeriosis infections, make L. monocytogenes of particular concern for manufacturers of cold-stored “ready to eat” (RTE foods. L. monocytogenes has been isolated from a wide variety of RTE foods and is responsible for several outbreaks associated with the consumption of RTE meat, poultry, dairy, fish and vegetable products. Although L. monocytogenes is among the most frequently-detected pathogens in dry fermented sausages, these products could be included in the category of RTE products in which the growth of L. monocytogenes is not favored and have rarely been implicated in listeriosis outbreaks. However, L. monocytogenes is highly difficult to control in fermented sausage processing environments due to its high tolerance to low pH and high salt concentration. In many Mediterranean-style dry fermented sausages, an empirical application of the hurdle technology often occurs and the frequent detection of L. monocytogenes in these products at the end of ripening highlights the need for food business operators to properly apply hurdle technology and to control the contamination routes of L. monocytogenes in the processing plants. In the following, through an up-to-date review of (personal and un- published data, the main aspects of the presence of L. monocytogenes in Mediterranean-style dry fermented sausages will be discussed.

The morphological, physiological and epidemiological features of L. monocytogenes, together with the severity of human listeriosis infections, make L. monocytogenes of particular concern for manufacturers of cold-stored "ready to eat" (RTE) foods. L. monocytogenes has been isolated from a wide variety of RTE foods and is responsible for several outbreaks associated with the consumption of RTE meat, poultry, dairy, fish and vegetable products. Although L. monocytogenes is among the most frequently-detected pathogens in dry fermented sausages, these products could be included in the category of RTE products in which the growth of L. monocytogenes is not favored and have rarely been implicated in listeriosis outbreaks. However, L. monocytogenes is highly difficult to control in fermented sausage processing environments due to its high tolerance to low pH and high salt concentration. In many Mediterranean-style dry fermented sausages, an empirical application of the hurdle technology often occurs and the frequent detection of L. monocytogenes in these products at the end of ripening highlights the need for food business operators to properly apply hurdle technology and to control the contamination routes of L. monocytogenes in the processing plants. In the following, through an up-to-date review of (personal and un-) published data, the main aspects of the presence of L. monocytogenes in Mediterranean-style dry fermented sausages will be discussed.

A case of Listeria monocytogenes induced spontaneous bacterial peritonitis (SBP) is reported in a patient with primary biliary cirrhosis. It is an indolent illness and may not show a neutrophil reaction in peritoneal fluid. Enrichment broth was required to isolate L monocytogenes in the patient. This is not routinely used in the UK and therefore isolates may be missed. L monocytogenes remains sensitive to ampicillin, penicillin and gentamicin, but is resistant to cephalosporin antibiotics. The rising incidence of listeriosis in the population suggests that the incidence of SBP from L monocytogenes is likely to increase.

Full Text Available Activation of the Nlrc4 inflammasome results in the secretion of IL-1β and IL-18 through caspase-1 and induction of pyroptosis. L. monocytogenes engineered to activate Nlrc4 by expression of Legionella pneumophilia flagellin (L. monocytogenes L.p.FlaA are less immunogenic for CD8(+ T cell responses than wt L. monocytogenes. It is also known that IL-1β orchestrates recruitment of myelomonocytic cells (MMC, which have been shown to interfere with T cell-dendritic cells (DC interactions in splenic white pulp (WP, limiting T cell priming and protective immunity. We have further analyzed the role of MMCs in the immunogenicity of L. monocytogenes L.p.FlaA. We confirmed that MMCs infiltrate the WP between 24-48 hours in response to wt L. monocytogenes infection and that depletion of MMCs enhances CD8(+ T cell priming and protective memory. L. monocytogenes L.p.FlaA elicited accelerated recruitment of MMCs into the WP. While MMCs contribute to control of L. monocytogenes L.p.FlaA, MMC depletion did not increase immunogenicity of L.p.FlaA expressing strains. There was a significant decrease in L. monocytogenes L.p.FlaA in CD8α(+ DCs independent of MMCs. These findings suggest that limiting inflammasome activation is important for bacterial accumulation in CD8α(+ DCs, which are known to be critical for T cell response to L. monocytogenes.

Full Text Available The foodborne pathogen Listeria monocytogenes has the capacity to survive and grow in a diverse range of natural environments. The transition from a food environment to the gastrointestinal tract begins a process of adaptation that may culminate in invasive systemic disease. Here we describe recent advances in our understanding of how L. monocytogenes adapts to the gastrointestinal environment prior to initiating systemic infection. We will discuss mechanisms used by the pathogen to survive encounters with acidic environments (which include the glutamate decarboxylase and arginine deiminase systems, and those which enable the organism to cope with bile acids (including bile salt hydrolase and competition with the resident microbiota. An increased understanding of how the pathogen survives in this environment is likely to inform the future design of novel prophylactic approaches that exploit specific pharmabiotics; including probiotics, prebiotics or phages.

Full Text Available Listeria monocytogenes is included in the foodborne pathogen, which has been associated with severaloutbreaks of human listeriosis especially in high risk groups. Listeria monocytogenes could be found inGouda cheeses because of poor hygienic and sanitation practices. In addition, this bacteria could surviveduring the making of cheese and cheese ripening process. The purpose of this study was to identify thepresence of L. monocytogenes in local and imported Gouda cheeses and how the safety level of the Goudacheese against contamination of L. monocytogenes. This study used the conventional method in accordancewith the Bacteriological Analytical Manual, US Food and Drug Administration and Bergey’s Manual ofDeterminative Bacteriology to detect the presence of L. monocytogenes at 15 samples of local Gouda cheeseand 15 samples of imported Gouda cheese sold in supermarkets in Jakarta and Bogor. The results of thisstudy showed that was not found L. monocytogenes in local and imported Gouda cheese. It could be concludedthat is Gouda cheese relatively safe from L. monocytogenes and meets Indonesian National Standard.

Significant food-borne disease outbreaks have occurred from consumption of ready-to-eat foods, including produce, contaminated with Listeria monocytogenes. Challenging food matrices (e.g., cantaloupe, sprouts) with limited processing steps postharvest to reduce pathogen loads have underscored a need for new mitigation strategies. Chlorine dioxide (ClO2) is increasingly being used in produce and other food systems to reduce food-borne pathogen levels. The goal of this study was to characterize the transcriptional response and survival of L. monocytogenes 10403S exposed to ClO2. The transcriptional profile of log-phase cells exposed to 300 mg/liter ClO2 for 15 min was defined by whole-genome microarray. A total of 340 genes were significantly differentially expressed. Among the differentially expressed genes, 223 were upregulated (fold change ≥ 1.5; adjusted P value < 0.05) in role categories responsible for protein fate, cellular processes, and energy metabolism. There were 113 and 16 genes differentially expressed belonging to regulatory networks of σ(B) and CtsR, respectively. We assessed L. monocytogenes 10403S survival after exposure to 100, 300, and 500 mg/liter aqueous ClO2 in brain heart infusion (BHI) broth; there was a significant difference between cells exposed to 500 mg/liter ClO2 and those exposed to all other conditions over time (P value < 0.05). Isogenic ΔsigB and ΔctsR mutants exposed to 300 mg/liter ClO2 were more sensitive to ClO2 than the wild type under the same conditions. These results provide an initial insight into the mechanisms that L. monocytogenes employs to survive sublethal ClO2 and further our understanding of the inactivation mechanisms of this increasingly used sanitizer.

Full Text Available Listeria monocytogenes is a Gram-positive pathogen responsible for the manifestation of human listeriosis, an opportunistic foodborne disease with an associated high mortality rate. The key to the pathogenesis of listeriosis is the capacity of this bacterium to trigger its internalization by non-phagocytic cells and to survive and even replicate within phagocytes. The arsenal of virulence proteins deployed by L. monocytogenes to successfully promote the invasion and infection of host cells has been progressively unveiled over the past decades. A large majority of them are located at the cell envelope, which provides an interface for the establishment of close interactions between these bacterial factors and their host targets. Along the multistep pathways carrying these virulence proteins from the inner side of the cytoplasmic membrane to their cell envelope destination, a multiplicity of auxiliary proteins must act on the immature polypeptides to ensure that they not only maturate into fully functional effectors but also are placed or guided to their correct position in the bacterial surface. As the major scaffold for surface proteins, the cell wall and its metabolism are critical elements in listerial virulence. Conversely, the crucial physical support and protection provided by this structure make it an ideal target for the host immune system. Therefore, mechanisms involving fine modifications of cell envelope components are activated by L. monocytogenes to render it less recognizable by the innate immunity sensors or more resistant to the activity of antimicrobial effectors. This review provides a state-of-the-art compilation of the mechanisms used by L. monocytogenes to organize its surface for virulence, with special focus on those proteins that work behind the frontline, either supporting virulence effectors or ensuring the survival of the bacterium within its host.

Listeria monocytogenes is a Gram-positive pathogen responsible for the manifestation of human listeriosis, an opportunistic foodborne disease with an associated high mortality rate. The key to the pathogenesis of listeriosis is the capacity of this bacterium to trigger its internalization by non-phagocytic cells and to survive and even replicate within phagocytes. The arsenal of virulence proteins deployed by L. monocytogenes to successfully promote the invasion and infection of host cells has been progressively unveiled over the past decades. A large majority of them is located at the cell envelope, which provides an interface for the establishment of close interactions between these bacterial factors and their host targets. Along the multistep pathways carrying these virulence proteins from the inner side of the cytoplasmic membrane to their cell envelope destination, a multiplicity of auxiliary proteins must act on the immature polypeptides to ensure that they not only maturate into fully functional effectors but also are placed or guided to their correct position in the bacterial surface. As the major scaffold for surface proteins, the cell wall and its metabolism are critical elements in listerial virulence. Conversely, the crucial physical support and protection provided by this structure make it an ideal target for the host immune system. Therefore, mechanisms involving fine modifications of cell envelope components are activated by L. monocytogenes to render it less recognizable by the innate immunity sensors or more resistant to the activity of antimicrobial effectors. This review provides a state-of-the-art compilation of the mechanisms used by L. monocytogenes to organize its surface for virulence, with special focus on those proteins that work “behind the frontline”, either supporting virulence effectors or ensuring the survival of the bacterium within its host. PMID:24809022

Among bacteria that reach the central nervous system (CNS), Listeria monocytogenes (Lm) is one of deadliest, in human and ruminant. This facultative intracellular bacterium has the particularity to induce meningitis, meningoencephalitis and rhombencephalitis. Mechanisms by which Lm accesses the CNS remain poorly understood, but two major routes of infection have been proposed, based on clinical, in vitro and in vivo observations. A retrograde neural route is likely to occur in ruminants upon ...

Full Text Available Listeria monocytogenes is a foodborne human pathogen that can cause invasive infection in susceptible animals and humans. For proliferation within hosts, this facultative intracellular pathogen uses a reservoir of specific metabolic pathways, transporter and enzymatic functions whose expression requires the coordinated activity of a complex regulatory network. The highly adapted metabolism of L. monocytogenes strongly depends on the nutrient composition of various milieus encountered during infection. Transcriptomic and proteomic studies revealed the spatial-temporal dynamic of gene expression of this pathogen during replication within cultured cells or in vivo. Metabolic clues are the utilization of unusual C2- and C3-bodies, the metabolism of pyruvate, thiamine availability, the uptake of peptides, the acquisition or biosynthesis of certain amino acids, and the degradation of glucose-phosphate via the pentose phosphate pathway. These examples illustrate the interference of in vivo conditions with energy, carbon and nitrogen metabolism, thus affecting listerial growth. The exploitation, analysis and modelling of the available data sets served as a first attempt to a systemic understanding of listerial metabolism during infection. L. monocytogenes might serve as a model organism for systems biology of a Gram-positive, facultative intracellular bacterium.

Detection of Listeria monocytogenes in food is currently based on enrichment methods. When L. monocytogenes is present with other Listeria species in food, the species compete during the enrichment process. Overgrowth competition of the nonpathogenic Listeria species might result in false-negative results obtained with the current reference methods. This potential issue was noted when 50 food samples artificially spiked with L. monocytogenes were tested with a real-time PCR assay and Canada's current reference method, MFHPB-30. Eleven of the samples studied were from foods naturally contaminated with Listeria species other than those used for spiking. The real-time PCR assay detected L. monocytogenes in all 11 of these samples; however, only 6 of these samples were positive by the MFHPB-30 method. To determine whether L. monocytogenes detection can be affected by other species of the same genus due to competition, an L. monocytogenes strain and a Listeria innocua strain with a faster rate of growth in the enrichment broth were artificially coinoculated at different ratios into ground pork meat samples and cultured according to the MFHPB-30 method. L. monocytogenes was detected only by the MFHPB-30 method when L. monocytogenes/L. innocua ratios were 6.0 or higher. In contrast, using the same enrichments, the real-time PCR assay detected L. monocytogenes at ratios as low as 0.6. Taken together, these findings support the hypothesis that L. monocytogenes can be outcompeted by L. innocua during the MFHPB-30 enrichment phase. However, more reliable detection of L. monocytogenes in this situation can be achieved by a PCR-based method mainly because of its sensitivity.

Inflammasomes are cytosolic innate immune surveillance systems that recognize a variety of danger signals, including those from pathogens. Listeria monocytogenes is a Gram-positive intracellular bacterium evolved to live within the harsh environment of the host cytosol. Further, L. monocytogenes can activate a robust cell-mediated immune response that is being harnessed as an immunotherapeutic platform. Access to the cytosol is critical for both causing disease and for inducing a protective immune response, and it is hypothesized that the cytosolic innate immune system, including the inflammasome, is critical for both host protection and induction of long term immunity. L. monocytogenes can activate a variety of inflammasomes via its pore-forming toxin Listeriolysin-O, flagellin, or DNA released through bacteriolysis; however, inflammasome activation attenuates L. monocytogenes, and as such, L. monocytogenes has evolved a variety of ways to limit inflammasome activation. Surprisingly, inflammasome activation also impairs the host cell-mediated immune response. Thus understanding how L. monocytogenes activates or avoids detection by the inflammasome is critical to understand the pathogenesis of L. monocytogenes and improve the cell-mediated immune response generated to L. monocytogenes for more effective immunotherapies. PMID:27460808

The stability of acid stress adaptation in Listeria monocytogenes and its induced cross protection effect against GRAS (generally recognized as safe) antimicrobial compounds has never been investigated before. In the present study, the acid stress adaptation in L. monocytogenes was initially induced...

The temperature-dependent alteration of flagellar motility gene expression is critical for the foodborne pathogen Listeria monocytogenes to respond to a changing environment. In this study, a genetic determinant, L. monocytogenes f2365_0220 (lmof2365_0220), encoding a putative protein that is struct...

A simple kinematic model for the trajectories of Listeria monocytogenes is generalized to a dynamical system rich enough to exhibit the resonant Hopf bifurcation structure of excitable media and simple enough to be studied geometrically. It is shown how L. monocytogenes trajectories and meandering spiral waves are organized by the same type of attracting set.

Several factors play critical roles in controlling the induction of acid-stress adaptation in L. monocytogenes. Our findings show that temperature plays a significant role in the induction of acid-stress adaptation in Listeria monocytogenes and two distinct patterns were observed: (I) Presence of su...

In this thesis, Listeria monocytogenes, a bacterial pathogen was studied, with emphasis on the detection and behaviour in food and environment.Epidemics of foodborne listeriosis have raised concern about the incidence of L. monocytogenes in foods. In the past 10-15 years listeriosis has emerged as a

The foodborne pathogen Listeria monocytogenes has the ability to produce biofilms in food-processing environments and then contaminate food products, which is a major concern for food safety. The biofilm forming behavior of 143 L. monocytogenes strains was determined in four different media that wer

Although several plasmids have been used in Listeria monocytogenes for generating mutants by allelic exchange, construction of L. monocytogenes mutants has been inefficient due to lack of effective selection markers for first and second recombination events. To address this problem, we have develope...

Listeria monocytogenes, a well-described cause of encephalitis and abortion in ruminants and of food-borne illness in humans, is rarely associated with disease in companion animals. A case of urinary tract infection associated with an atypical, weakly hemolytic L. monocytogenes strain is described i...

The objective of this research is to determine the thermal inactivation kinetics of Listeria monocytogenes in chicken breast meat using both isothermal and dynamic conditions. A four-strain cocktail of L. monocytogenes was inoculated to chicken breast meat. Isothermal studies were performed by sub...

Population diversity and the ability to adapt to changing environments allow Listeria monocytogenes to grow and survive under a wide range of environmental conditions. In this study, we aimed to evaluate the performance of a set of acid resistant L. monocytogenes variants in mixed-species biofilms w

Sublethal concentrations of ethanol or isopropanol increased attachment of Listeria monocytogenes at 10, 20, or 30 degrees C; no induction occurred at 37 degrees C. The alcohol induction phenotype was retained in sigB and cesRK mutants; however, the degree of induction was affected. These results suggest that alcohol may contribute to the persistence of L. monocytogenes.

Listeria monocytogenes is an important foodborne pathogen that has been responsible for severe infections in humans. The ubiquitous distribution of L. monocytogenes in the environment and its ability to grow at refrigeration temperature and at high osmolarity are of paramount importance for its haz

The naturally occurring compatible solutes betaine and L-carnitine allow the food-borne pathogen Listeria monocytogenes to adjust to environments of high osmotic strength. Previously, it was demonstrated that L. monocytogenes possesses an ATP-dependent L-carnitine transporter. The present study

The fate of 3 different Listeria monocytogenes strains (Scott A, 2F and 6E) was studied independently in brine and on factory-scale Gouda cheeses that had been submerged in brine that was artificially contaminated with these individual strains. Viable numbers of L. monocytogenes in the brine

The foodborne pathogen Listeria monocytogenes has the ability to produce biofilms in food-processing environments and then contaminate food products, which is a major concern for food safety. The biofilm forming behavior of 143 L. monocytogenes strains was determined in four different media that

This paper shortly summarizes data related to risk assessment of Listeria monocytogenes. From available data on risk assessment, it is concluded that the levels of L. monocytogenes consumed is an important factor affecting the incidence of listeriosis. Foods that do not support the growth of L. m...

A recent outbreak linked to whole cantaloupes underscores the importance of understanding growth kinetics of Listeria monocytogenes in cut melons at different temperatures. Whole cantaloupe, watermelon, and honeydew purchased from a local supermarket were cut into 10 ± 1 g cubes. A four-strain cocktail of L. monocytogenes from food related outbreaks was used to inoculate fruit, resulting in ~10(3) CFU/10 g. Samples were stored at 4, 10, 15, 20, or 25 °C and L. monocytogenes were enumerated at appropriate time intervals. The square root model was used to describe L. monocytogenes growth rate as a function of temperature. The model was compared to prior models for Salmonella and Escherichia coli O157:H7 growth on cut melon, as well as models for L. monocytogenes on cantaloupe and L. monocytogenes ComBase models. The current model predicts faster growth of L. monocytogenes vs. Salmonella and E. coli O157:H7 at temperatures below 20 °C, and agrees with estimates from ComBase Predictor, and a corrected published model for L. monocytogenes on cut cantaloupe. The model predicts ~4 log CFU increase following 15 days at 5 °C, and ∼1 log CFU increase following 6 days at 4 °C. The model can also be used in subsequent quantitative microbial risk assessments.

Listeria monocytogenes is a Gram-positive, facultative intracellular and invasive bacterium that has tropism to the placenta, and causes fetal morbidity and mortality in several mammalian species. While infection with L. monocytogenes and L. ivanovii are known as important causes of abortion and reproductive failure in cattle, the pathogenesis of maternal-fetal listeriosis in this species is poorly known. This study used the bovine chorioallantoic membrane explant model to investigate the kinetics of L. monocytogenes, L. ivanovii, and L. innocua infections in bovine trophoblastic cells for up to 8 h post infection. L. monocytogenes and L. ivanovii were able to invade and multiply in trophoblastic cells without causing cell death or inducing expression of pro-inflammatory genes. Although L. innocua was unable to multiply in bovine trophoblastic cells, it induced transcription of the pro-inflammatory mediator CXCL6. This study demonstrated for the first time the susceptibility of bovine trophoblastic cells to L. monocytogenes and L. ivanovii infection.

The ability of the pediocin AcH producing Lactobacillus plantarum DDEN 11007 and its non-producing plasmid-cured isogenic variant, DDEN 12305 to prevent the persistence and growth of Listeria monocytogenes EP2 in two gastrointestinal (GI) tract models was examined. In vitro studies conducted...... in a two-stage continuous flow system showed that L. plantarum DDEN 11007 inhibited L. monocytogenes EP2 under these conditions, while less effect was seen of the non-bacteriocin producing variant. The inhibitory effect was more pronounced at pH 5 than at pH 7. No effect on persistence of L. monocytogenes...... in the GI tract was seen in gnotobiotic rats colonized with either the pediocin AcH producing or the non-bacteriocin producing variant of L. plantarum when compared to rats inoculated with L. monocytogenes EP2 alone. Surprisingly, inoculation of the gnotobiotic animals with either of the L. plantarum...

A lactic acid bacterium with high tolerance of temperature and lignocellulose derived inhibitor was isolated and characterized as Pediococcus acidilactici DQ2. The strain used in the simultaneous saccharification and fermentation (SSF) for high titer lactic acid production at the high solids loading of corn stover. Corn stover was pretreated using the dry sulphuric acid pretreatment, followed by a biological detoxification to remove the inhibitors produced in the pretreatment. The bioreactor with a novel helical impeller was used to the SSF operation of the pretreated and biodetoxified corn stover. The results show that a typical SSF operation at 48 °C, pH 5.5, and near 30% (w/w) solids loading in both 5 and 50 L bioreactors was demonstrated. The lactic acid titer, yield, and productivity reached 101.9 g/L, 77.2%, and 1.06 g/L/h, respectively. The result provided a practical process option for cellulosic lactic acid production using virgin agriculture lignocellulose residues.

Daqu, a traditional fermentation starter that is used for Chinese liquor and vinegar production, is still manufactured through a traditional spontaneous solid-state fermentation process with no selected microorganisms are intentionally inoculated. The aim of this work was to analyze the microbiota dynamics during the solid-state fermentation process of Daqu using a traditional and bioaugmented inoculation with autochthonous of Bacillus, Pediococcus, Saccharomycopsis and Wickerhamomyces at an industrial scale. Highly similar dynamics of physicochemical parameters, enzymatic activities and microbial communities were observed during the traditional and bioaugmented solid-state fermentation processes. Both in the two cases, groups of Streptophyta, Rickettsiales and Xanthomonadales only dominated the first two days, but Bacillales and Eurotiales became predominant members after 2 and 10 days fermentation, respectively. Phylotypes of Enterobacteriales, Lactobacillales, Saccharomycetales and Mucorales dominated the whole fermentation process. No significant difference (P > 0.05) in microbial structure was observed between the traditional and bioaugmented fermentation processes. However, slightly higher microbial richness was found during the bioaugmented fermentation process after 10 days fermentation. Our results reinforced the microbiota dynamic stability during the solid-state fermentation process of Daqu, and might aid in controlling the traditional Daqu manufacturing process.

Full Text Available As the number of bacterial genomes increases dramatically, the demand for easy to use tools with transparent functionality and comprehensible output for applied comparative genomics grows as well. We present BlAst Diagnostic Gene findEr (BADGE, a tool for the rapid prediction of diagnostic marker genes (DMGs for the differentiation of bacterial groups (e.g. pathogenic / nonpathogenic. DMG identification settings can be modified easily and installing and running BADGE does not require specific bioinformatics skills. During the BADGE run the user is informed step by step about the DMG finding process, thus making it easy to evaluate the impact of chosen settings and options. On the basis of an example with relevance for beer brewing, being one of the oldest biotechnological processes known, we show a straightforward procedure, from phenotyping, genome sequencing, assembly and annotation, up to a discriminant marker gene PCR assay, making comparative genomics a means to an end. The value and the functionality of BADGE were thoroughly examined, resulting in the successful identification and validation of an outstanding novel DMG (fabZ for the discrimination of harmless and harmful contaminations of Pediococcus damnosus, which can be applied for spoilage risk determination in breweries. Concomitantly, we present and compare five complete P. damnosus genomes sequenced in this study, finding that the ability to produce the unwanted, spoilage associated off-flavor diacetyl is a plasmid encoded trait in this important beer spoiling species.

As the number of bacterial genomes increases dramatically, the demand for easy to use tools with transparent functionality and comprehensible output for applied comparative genomics grows as well. We present BlAst Diagnostic Gene findEr (BADGE), a tool for the rapid prediction of diagnostic marker genes (DMGs) for the differentiation of bacterial groups (e.g. pathogenic / nonpathogenic). DMG identification settings can be modified easily and installing and running BADGE does not require specific bioinformatics skills. During the BADGE run the user is informed step by step about the DMG finding process, thus making it easy to evaluate the impact of chosen settings and options. On the basis of an example with relevance for beer brewing, being one of the oldest biotechnological processes known, we show a straightforward procedure, from phenotyping, genome sequencing, assembly and annotation, up to a discriminant marker gene PCR assay, making comparative genomics a means to an end. The value and the functionality of BADGE were thoroughly examined, resulting in the successful identification and validation of an outstanding novel DMG (fabZ) for the discrimination of harmless and harmful contaminations of Pediococcus damnosus, which can be applied for spoilage risk determination in breweries. Concomitantly, we present and compare five complete P. damnosus genomes sequenced in this study, finding that the ability to produce the unwanted, spoilage associated off-flavor diacetyl is a plasmid encoded trait in this important beer spoiling species. PMID:27028007

Full Text Available Three lactic acid bacterial strains, Lactobacillus plantarum, HK006, and HK109, and Pediococcus pentosaceus PP31 exhibit probiotic potential as antiallergy agents, both in vitro and in vivo. However, the safety of these new strains requires evaluation when isolated from infant faeces or pickled cabbage. Multiple strains (HK006, HK109, and PP31 were subject to a bacterial reverse mutation assay and a short-term oral toxicity study. The powder product exhibited mutagenic potential in Salmonella Typhimurium strains TA98 and TA1535 (with or without metabolic activation. In the short-term oral toxicity study, rats received a normal dosage of 390 mg/kg/d (approximately 9×109 CFU/kg/d or a high dosage of 1950 mg/kg/d (approximately 4.5×1010 CFU/kg/d for 28 d. No adverse effects were observed regarding the general condition, behaviour, growth, feed and water consumption, haematology, clinical chemistry indices, organ weights, or histopathologic analysis of the rats. These studies have demonstrated that the consumption of multiple bacterial strains is not associated with any signs of mutagenicity of S. Typhimurium or toxicity in Wistar rats, even after consuming large quantities of bacteria.

As the number of bacterial genomes increases dramatically, the demand for easy to use tools with transparent functionality and comprehensible output for applied comparative genomics grows as well. We present BlAst Diagnostic Gene findEr (BADGE), a tool for the rapid prediction of diagnostic marker genes (DMGs) for the differentiation of bacterial groups (e.g. pathogenic / nonpathogenic). DMG identification settings can be modified easily and installing and running BADGE does not require specific bioinformatics skills. During the BADGE run the user is informed step by step about the DMG finding process, thus making it easy to evaluate the impact of chosen settings and options. On the basis of an example with relevance for beer brewing, being one of the oldest biotechnological processes known, we show a straightforward procedure, from phenotyping, genome sequencing, assembly and annotation, up to a discriminant marker gene PCR assay, making comparative genomics a means to an end. The value and the functionality of BADGE were thoroughly examined, resulting in the successful identification and validation of an outstanding novel DMG (fabZ) for the discrimination of harmless and harmful contaminations of Pediococcus damnosus, which can be applied for spoilage risk determination in breweries. Concomitantly, we present and compare five complete P. damnosus genomes sequenced in this study, finding that the ability to produce the unwanted, spoilage associated off-flavor diacetyl is a plasmid encoded trait in this important beer spoiling species.

Occurrence of feruloyl-CoA synthetase (fcs) and enoyl-CoA hydratase (ech) genes responsible for the bioconversion of ferulic acid to vanillin have been reported and characterized from Amycolatopsis sp., Streptomyces sp., and Pseudomonas sp. Attempts have been made to express these genes in Escherichia coli DH5α, E. coli JM109, and Pseudomonas fluorescens. However, none of the lactic acid bacteria strain having GRAS status was previously proposed for heterologous expression of fcs and ech genes for production of vanillin through biotechnological process. Present study reports heterologous expression of vanillin synthetic gene cassette bearing fcs and ech genes in a dairy isolate Pediococcus acidilactici BD16. After metabolic engineering, statistical optimization of process parameters that influence ferulic acid to vanillin biotransformation in the recombinant strain was carried out using central composite design of response surface methodology. After scale-up of the process, 3.14 mM vanillin was recovered from 1.08 mM ferulic acid per milligram of recombinant cell biomass within 20 min of biotransformation. From LCMS-ESI spectral analysis, a metabolic pathway of phenolic biotransformations was predicted in the recombinant P. acidilactici BD16 (fcs (+)/ech (+)).

The present study was aimed to characterize physico-chemical and microbial population of distillery effluent and isolate a novel thermotolerant bacterium for color, COD, and BOD reduction of spentwash. The level of alkalinity, TSS, DO, COD, BOD, TN, ammonical nitrogen, nitrate nitrogen, phosphorous, potassium, chloride, and calcium of spentwash (SW), bioreactor effluent (BE), and secondary treated effluent (STE) were well above the permissible limits. The level of color, TS, and TDS were under the permissible limits for STE but not for SW and BE. The microbial population was higher in BE. The results revealed that effluent was highly polluted and require suitable treatment before discharge. A novel thermotolerant bacterium, identified as Pediococcus acidilactici, was isolated which exhibited maximum 79 % decolorization, 85 % COD, and 94 % BOD reduction at 45 °C using 0.1 %, glucose; 0.1 %, peptone; 0.05 %, MgSO4; 0.05 %, K2HPO4; pH 6.0 within 24 h under static condition. The ability of this strain to decolorize melanoidin at minimum carbon and nitrogen supplementation warrants its possible application for effluent treatment at industrial level. In addition, it is first instance when melanoidin decolorization was reported by P. acidilactici. This study could be an approach towards control of environmental pollution and health hazards of people in and around the effluent distillery unit.

The aim was to produce Nham that was enriched with γ-aminobutyric acid (GABA); therefore two GABA producing lactic acid bacteria (Pediococcus pentosaceus HN8 and Lactobacillus namurensis NH2) were used as starter cultures. By using the central composite design (CCD) we showed that addition of 0.5% monosodium glutamate (MSG) together with an inoculum size of roughly 6logCFU/g of each of the two strains produced a maximal amounts of GABA (4051 mg/kg) in the 'GABA Nham' product. This was higher than any current popular commercial Nham product by roughly 8 times. 'GABA Nham' with the additions of both starters and MSG (TSM) supported maximum populations of lactic acid bacteria (LAB) with a minimum of yeasts and no staphylococci or molds when compared to the controls that had no addition of any starters or MSG (TNN), or only the addition of MSG (TNM), or with only the starter (TSN). Based on proximate analysis among the Nham sets, 'GABA Nham' was low in fat, carbohydrate and energy although its texture and color were slightly different from the control (TNN). However, sensory evaluations of 'GABA Nham' were more acceptable than the controls and commercial Nham products for all tested parameters. Hence, a unique novel 'GABA Nham' fermented pork sausage was successfully developed.

Pediococcus acidilactici ATCC 8042 and Enterococcus faecium NRRL B-2354 were investigated as potential surrogates for Salmonella serovars using thermal death time kinetics in products such as dry pet foods. The D-values of P. acidilactici ATCC 8042, E. faecium NRRL B-2354, and a cocktail of seven Salmonella serovars associated with low-moisture products were determined in a preservative-free dry pet food product at moisture levels of 9.1, 17.9, and 27.0% and heated between 76.7 and 87.8°C. The D-values were calculated by least squares linear regression. The D-values of P. acidilactici ATCC 8042 were higher than those for the Salmonella serovar cocktail but lower than those for E. faecium NRRL 2354. At 9.1% moisture, D-values of 6.54, 11.51, and 11.66 min at 76.7°C, 2.66, 3.22, and 4.08 min at 82.2°C, and 1.07, 1.29, and 1.69 min at 87.8°C were calculated for Salmonella serovars, P. acidilactici ATCC 8042, and E. faecium NRRL B-2354, respectively. The data suggest that the thermal inactivation characteristics of P. acidilactici ATCC 8042 can be utilized as a surrogate to predict the response of Salmonella in dry pet food products that are thermally processed at <90°C.

Green terror fish were fed for two months with three types of feed including: control diet (C), diet containing 2% fish oil (O) and diet containing fish oil supplemented with 0.1% Pediococcus acidilactici bacteria (PA). At the end of the feeding period, 50 fish of different groups (n = 3) with an average weight of 4.28 g were transferred to 9 tank. Hypoxia tests were set out by sampling at three times including before hypoxia (BH) initiation, hypoxia stress spot (H) and starting mortality (SM). In fish submitted to the diet containing P. acidilactici bacteria, the immune indices of lysozyme activity (4.08, 4.19 and 4.85 μg/ml)], complement activity (2.65, 2.77 and 2.1 U/ml) and total immunoglobulin (10.05, 10.25 and 9.9 μg/ml) improved in all stages of sampling (BH, H and SM), respectively (p terror fish.

Full Text Available The aim of this study was to evaluate the probiotic properties of Pediococcus acidilactici B14 and to study its resistance in the gastrointestinal system when combined with Lactobacillus acidophilus ATCC 4356 and used in a potentially symbiotic aerated soy based dessert. P. acidilactici B14 showed some important probiotic characteristics such as survival rate of 45.9% at pH 2.5; 72.4% in 0.3% bile salts and 95.8% after gastrointestinal transit at pH 4.0. Tolerance against the antibiotics cephalexin, neomycin, vancomycin, cefotaxime and penicillin G was also observed. The strain inhibited antagonism against the following cultures: Escherichia coli ATCC 25922, Bacillus cereus ATCC 33018, Staphylococcus aureus ATCC 6538P and Salmonella sp. The mixed culture of P. acidilactici B14 with L. acidophilus ATCC 4356 showed a survival rate of 92.4% after the passage through the gastrointestinal system at pH 4.0. Furthermore, in the presence of the food matrix, an average increase in cell viability, after being subjected to the gastrointestinal system of 9.9% at pH 2.0 and 6.1% at pH 4.0, was observed. This characterized the adequacy of the associated culture as probiotic in the development of a functional food such as soy based aerated symbiotic dessert.

Full Text Available The objective of this study was to produce phage display-derived binders with the ability to distinguish Listeria monocytogenes from other Listeria spp., which may have potential utility to enhance detection of Listeria monocytogenes. To obtain binders with the desired binding specificity a series of surface and solution phage-display biopannings were performed. Initially, three rounds of surface biopanning against gamma-irradiated L. monocytogenes serovar 4b cells were performed followed by an additional surface biopanning round against L. monocytogenes 4b which included prior subtraction biopanning against gamma-irradiated L. innocua cells. In an attempt to further enhance binder specificity for L. monocytogenes 4b two rounds of solution biopanning were performed, both rounds included initial subtraction solution biopanning against L. innocua. Subsequent evaluations were performed on the phage clones by phage binding ELISA. All phage clones tested from the second round of solution biopanning had higher specificity for L. monocytogenes 4b than for L. innocua and three other foodborne pathogens (Salmonella spp., Escherichia coli and Campylobacter jejuni. Further evaluation with five other Listeria spp. revealed that one phage clone in particular, expressing peptide GRIADLPPLKPN, was highly specific for L. monocytogenes with at least 43-fold more binding capability to L. monocytogenes 4b than to any other Listeria sp. This proof-of-principle study demonstrates how a combination of surface, solution and subtractive biopanning was used to maximise binder specificity. L. monocytogenes-specific binders were obtained which could have potential application in novel detection tests for L. monocytogenes, benefiting both the food and medical industries.

The objective of this study was to produce phage display-derived binders with the ability to distinguish Listeria monocytogenes from other Listeria spp., which may have potential utility to enhance detection of Listeria monocytogenes. To obtain binders with the desired binding specificity a series of surface and solution phage-display biopannings were performed. Initially, three rounds of surface biopanning against gamma-irradiated L. monocytogenes serovar 4b cells were performed followed by an additional surface biopanning round against L. monocytogenes 4b which included prior subtraction biopanning against gamma-irradiated L. innocua cells. In an attempt to further enhance binder specificity for L. monocytogenes 4b two rounds of solution biopanning were performed, both rounds included initial subtraction solution biopanning against L. innocua. Subsequent evaluations were performed on the phage clones by phage binding ELISA. All phage clones tested from the second round of solution biopanning had higher specificity for L. monocytogenes 4b than for L. innocua and three other foodborne pathogens (Salmonella spp., Escherichia coli and Campylobacter jejuni). Further evaluation with five other Listeria spp. revealed that one phage clone in particular, expressing peptide GRIADLPPLKPN, was highly specific for L. monocytogenes with at least 43-fold more binding capability to L. monocytogenes 4b than to any other Listeria sp. This proof-of-principle study demonstrates how a combination of surface, solution and subtractive biopanning was used to maximise binder specificity. L. monocytogenes-specific binders were obtained which could have potential application in novel detection tests for L. monocytogenes, benefiting both the food and medical industries.

Full Text Available L. monocytogenes has been established in different plants for the production of food, including dairy plants, abattoirs, plants for the processing of fish, as well as those for the production of ready-to-eat (RTE food and this fact is being considered as the primary mechanism of food contamination with this bacteria. There is also the factor of numerous and diverse contaminated production equipment, because it has certain parts that are inaccessible for the necessary cleaning and disinfection. The temperature, position, as well as the material of the work surface are also linked to the contamination of plants with this bacteria. Investigations carried out so far have helped toward the better understanding of the manner and time of contamination of food items in the course of the production process, but there are still unresolved problems, including most certainly the biggest one - the adherence of bacteria and the creation of a biofilm, when the bacteria is in that condition more resistant to so-called stress factors which are usually used in the food industry for the purpose of decontamination of the surfaces with which foods come into contact. The control of L. monocytogenes in food production plants is possible primarily by using an integrated programme, compatible with the systems Hazard Analysis Critical Control Point (HACCP and Good Hygiene Practice (GHP, necessary in the production of food that is safe for the consumer. Essentially, the control measures that can contribute to reducing the incidence of findings of L.monocytogenes in the finished product, as well as the reducing of the level of contamination with this bacteria are linked, on the one hand, with hygiene procedures in the production process, and, on the other, with the applied technological procedures.

This paper examines the synergistic action of carbon dioxide and nisin on Listeria monocytogenes Scott A wild-type and nisin-resistant (Nis(r)) cells grown in broth at 4 degrees C. Carbon dioxide extended the lag phase and decreased the specific growth rate of both strains, but to a greater degree...... for cultures in CO2. This synergism between nisin and CO2 was examined mechanistically by following the leakage of carboxyfluorescein (CF) from listerial liposomes. Carbon dioxide enhanced nisin-induced CF leakage, indicating that the synergistic action of CO2 and nisin occurs at the cytoplasmic membrane...

Fatty acids and monoglycerides were evaluated in brain heart infusion broth and in milk for antimicrobial activity against the Scott A strain of Listeria monocytogenes. C12:0, C18:3, and glyceryl monolaurate (monolaurin) had the strongest activity in brain heart infusion broth and were bactericidal at 10 to 20 micrograms/ml, whereas potassium (K)-conjugated linoleic acids and C18:2 were bactericidal at 50 to 200 micrograms/ml. C14:0, C16:0, C18:0, C18:1, glyceryl monomyristate, and glyceryl m...

DivIVA is a membrane binding protein that clusters at curved membrane regions such as the cell poles and the membrane invaginations occurring during cell division. DivIVA proteins recruit many other proteins to these subcellular sites through direct protein-protein interactions. DivIVA-dependent functions are typically associated with cell growth and division, even though species-specific differences in the spectrum of DivIVA functions and their causative interaction partners exist. DivIVA from the Gram-positive human pathogen Listeria monocytogenes has at least three different functions. In this bacterium, DivIVA is required for precise positioning of the septum at mid-cell, it contributes to secretion of autolysins required for breakdown of peptidoglycan at the septum after completion of cell division, and it is essential for flagellar motility. While the DivIVA interaction partners for control of division site selection are well-established, the proteins connecting DivIVA with autolysin secretion or swarming motility are completely unknown. We set out to identify divIVA alleles, in which these three DivIVA functions could be separated, since the question of the degree to which the three functions of L. monocytogenes DivIVA are interlinked could not be answered before. Here, we identify such alleles, and our results show that division site selection, autolysin secretion, and swarming represent three discrete pathways that are independently influenced by DivIVA. These findings provide the required basis for the identification of DivIVA interaction partners controlling autolysin secretion and swarming in the future.IMPORTANCE DivIVA of the pathogenic bacterium Listeria monocytogenes is a central scaffold protein that influences at least three different cellular processes, namely cell division, protein secretion and bacterial motility. How DivIVA coordinates these rather unrelated processes is not known. We here identify variants of L. monocytogenes DivIVA, in which

Full Text Available The aim of the present study is to investigate operative procedures that allow to minimize Listeria monocytogenes (L. m. hazard in the main traditional sausage of the internal areas of Marche (Italy: the Ciauscolo, that has received the quality trademark PGI. It is made from lean cuts of well mature pork that is finely minced, adding fat which give the salami his characteristic softness and flavour. It is characterized by having a very little maturing period that determine high aw levels and, for this peculiarity, it allows L. m development.

Full Text Available Listeria monocytogenes is an important foodborne pathogen implicated in many outbreaks of listeriosis. This study aimed at screening for the potential use of Rhodomyrtus tomentosa ethanolic leaf extract as a bio-control agent against L. monocytogenes. Twenty-two L. monocytogenes isolates were checked with 16 commercial antibiotics and isolates displayed resistance to 10 antibiotics. All the tested isolates were sensitive to the extract with inhibition zones ranging from 14 to 16 mm. Minimum inhibitory concentration (MIC and minimum bactericidal concentration (MBC values ranged from 16 to 32 µg/mL and 128 to 512 µg/mL, respectively. Time-kill assay showed that the extract had remarkable bactericidal effects on L. monocytogenes. The extract at a concentration of 16 µg/mL reduced tolerance to 10% NaCl in L. monocytogenes in 4 h. Stationary phase L. monocytogenes cells were rapidly inactivated by greater than 3-log units within 30 min of contact time with R. tomentosa extract at 128 µg/mL. Electron microscopy revealed fragmentary bacteria with changes in the physical and morphological properties. Our study demonstrates the potential of the extract for further development into a bio-control agent in food to prevent the incidence of L. monocytogenes contamination.

Cig kofte is a traditional Turkish food prepared from minced beef, bulgur, onions, garlic and varieties of spices. It is generally consumed within a few hours. However, leftovers can be kept in refrigerator or in room temperature up to 24h until they are consumed. In this study, survival and growth of two Listeria monocytogenes serotypes were investigated in cig kofte during the storage. For this purpose, the prepared samples were separately contaminated with serotypes 1/2b or 4b of L. monocytogenes at the level of 10(4)CFU/g and stored at 4°C and 21°C. L. monocytogenes colonies were counted at the beginning, 3rd, 6th, 12th and 24th hours of the storage. At 4°C, L. monocytogenes 4b significantly increased (P0.05) during the storage period. At 21°C, both L. monocytogenes 1/2b and 4b increased significantly (Pcig kofte did not inhibit the growths of L. monocytogenes serotypes during the storage. These results indicated that L. monocytogenes was able to survive and grow in cig kofte at the both storage temperatures of 4°C and 21°C and cig kofte seemed to be a suitable medium for this pathogen.

The objective of this study was to evaluate the relationship between prevalence of Listeria monocytogenes as an outcome and Listeria spp. as an explanatory variable by food products, food contact surfaces, and nonfood contact surfaces in seafood processing plants by using peer-reviewed published data. Nine sets of prevalence data of L. monocytogenes and Listeria spp. were collected from published studies and used for the analyses. Based on our analysis, the relationship between L. monocytogenes prevalence and Listeria spp. prevalence in food products (incoming raw materials and finish products) was significant (P = 0.04) with (low) R² = 0.36. Furthermore, Listeria spp. were not a good indicator for L. monocytogenes when testing food contact surfaces (R² = 0.10). Listeria spp. were a good indicator for L. monocytogenes only on nonfood contact surfaces (R² = 0.90). On the other hand, the presence of Listeria spp. on food contact surfaces (R² = 0.002) and nonfood contact surfaces (R² = 0.03) was not a good indicator for L. monocytogenes presence in food products. In general, prevalence of Listeria spp. does not seem to be a good indicator for L. monocytogenes prevalence in seafood processing plants.

Full Text Available Listeria monocytogenes, a gram-positive pathogen, and causative agent of listeriosis, has become a widely used model organism for intracellular infections. Recent studies have identified small non-coding RNAs (sRNAs as important factors for regulating gene expression and pathogenicity of L. monocytogenes. Increased speed and reduced costs of high throughput sequencing (HTS techniques have made RNA sequencing (RNA-Seq the state-of-the-art method to study bacterial transcriptomes. We created a large transcriptome dataset of L. monocytogenes containing a total of 21 million reads, using the SOLiD sequencing technology. The dataset contained cDNA sequences generated from L. monocytogenes RNA collected under intracellular and extracellular condition and additionally was size fractioned into three different size ranges from 150 nt. We report here, the identification of nine new sRNAs candidates of L. monocytogenes and a reevaluation of known sRNAs of L. monocytogenes EGD-e. Automatic comparison to known sRNAs revealed a high recovery rate of 55%, which was increased to 90% by manual revision of the data. Moreover, thorough classification of known sRNAs shed further light on their possible biological functions. Interestingly among the newly identified sRNA candidates are antisense RNAs (asRNAs associated to the housekeeping genes purA, fumC and pgi and potentially their regulation, emphasizing the significance of sRNAs for metabolic adaptation in L. monocytogenes.

Listeria monocytogenes, a gram-positive pathogen, and causative agent of listeriosis, has become a widely used model organism for intracellular infections. Recent studies have identified small non-coding RNAs (sRNAs) as important factors for regulating gene expression and pathogenicity of L. monocytogenes. Increased speed and reduced costs of high throughput sequencing (HTS) techniques have made RNA sequencing (RNA-Seq) the state-of-the-art method to study bacterial transcriptomes. We created a large transcriptome dataset of L. monocytogenes containing a total of 21 million reads, using the SOLiD sequencing technology. The dataset contained cDNA sequences generated from L. monocytogenes RNA collected under intracellular and extracellular condition and additionally was size fractioned into three different size ranges from 150 nt. We report here, the identification of nine new sRNAs candidates of L. monocytogenes and a reevaluation of known sRNAs of L. monocytogenes EGD-e. Automatic comparison to known sRNAs revealed a high recovery rate of 55%, which was increased to 90% by manual revision of the data. Moreover, thorough classification of known sRNAs shed further light on their possible biological functions. Interestingly among the newly identified sRNA candidates are antisense RNAs (asRNAs) associated to the housekeeping genes purA, fumC and pgi and potentially their regulation, emphasizing the significance of sRNAs for metabolic adaptation in L. monocytogenes. PMID:24498259

Full Text Available Listeria monocytogenes is a food-borne pathogen responsible for the potentially fatal disease listeriosis and terrestrial ecosystems have been hypothesized to be its natural reservoir. Therefore, identifying the key edaphic factors that influence its survival in soil is critical. We measured the survival of L. monocytogenes in a set of 100 soil samples belonging to the French Soil Quality Monitoring Network. This soil collection is meant to be representative of the pedology and land use of the whole French territory. The population of L. monocytogenes in inoculated microcosms was enumerated by plate count after 7, 14 and 84 days of incubation. Analysis of survival profiles showed that L. monocytogenes was able to survive up to 84 days in 71% of the soils tested, in the other soils (29% only a short-term survival (up to 7 to 14 days was observed. Using variance partitioning techniques, we showed that about 65% of the short-term survival ratio of L. monocytogenes in soils was explained by the soil chemical properties, amongst which the basic cation saturation ratio seems to be the main driver. On the other hand, while explaining a lower amount of survival ratio variance (11%, soil texture and especially clay content was the main driver of long-term survival of L. monocytogenes in soils. In order to assess the effect of the endogenous soils microbiota on L. monocytogenes survival, sterilized versus non-sterilized soils microcosms were compared in a subset of 9 soils. We found that the endogenous soil microbiota could limit L. monocytogenes survival especially when soil pH was greater than 7, whereas in acidic soils, survival ratios in sterilized and unsterilized microcosms were not statistically different. These results point out the critical role played by both the endogenous microbiota and the soil physic-chemical properties in determining the survival of L. monocytogenes in soils.

Full Text Available In the EU, food is considered safe with regard to Listeria monocytogenes if the number of micro-organisms does not exceed 100 colony forming units (cfu/g throughout its shelf-life. Therefore, it is important to determine if a food supports growth of L. monocytogenes. Guidelines for conducting challenge tests for growth assessment of L. monocytogenes on foods were published by the European Union Reference Laboratory (EURL in 2014. The aim of this study was to use these guidelines to determine if refrigerated, fresh, whole, closed-cap, prepackaged mushrooms (Agaricus bisporus support the growth of L. monocytogenes. Three batches of mushrooms were artificially inoculated at approximately 100 cfu/g with a three-strain mix of L. monocytogenes and incubated for 2 days at 8°C followed by 4 days at 12°C. L. monocytogenes numbers were determined (in triplicate for each batch on days 0, 2 and 6. Water activity, pH and total bacterial counts were also determined. There was no increase in the number of L. monocytogenes above the threshold of 0.5 log cfu/g in any of the replicates. In 8 of 9 replicates, the numbers decreased indicating that A. bisporus do not support the growth of L. monocytogenes. As the EU regulations allow < 100 cfu/g if the food cannot support growth of L. monocytogenes, the significance of this study is that mushrooms with < 100 cfu/g may be within the regulations and therefore, quantitative rather than qualitative determination may be required.

The main objective of this study was to investigate the growth kinetics of Listeria monocytogenes and background microorganisms in fresh-cut cantaloupe. Fresh-cut cantaloupe samples, inoculated with three main serotypes (1/2a, 1/2b, and 4b) of L. monocytogenes, were incubated at different temperatures, ranging from 4 to 43 °C, to develop kinetic growth models. During storage studies, the population of both background microorganisms and L. monocytogenes began to increase almost immediately, with little or no lag phase for most growth curves. All growth curves, except for two growth curves of L. monocytogenes 1/2a at 4 °C, developed to full curves (containing exponential and stationary phases), and can be described by a 3-parameter logistic model. There was no significant difference (P = 0.28) in the growth behaviors and the specific growth rates of three different serotypes of L. monocytogenes inoculated to fresh-cut cantaloupe. The effect of temperature on the growth of L. monocytogenes and spoilage microorganisms was evaluated using three secondary models. For L. monocytogenes, the minimum and maximum growth temperatures were estimated by both the Ratkowsky square-root and Cardinal parameter models, and the optimum temperature and the optimum specific growth rate by the Cardinal parameter model. An Arrhenius-type model provided more accurate estimation of the specific growth rate of L. monocytogenes at temperatures <4 °C. The kinetic models developed in this study can be used by regulatory agencies and food processors for conducting risk assessment of L. monocytogenes in fresh-cut cantaloupe, and for estimating the shelf-life of fresh-cut products.

The VIDAS Listeria monocytogenes Xpress (LMX) test is an enzyme-linked fluorescent immunoassay designed for use with the automated VIDAS or mini-VIDAS instruments for the specific detection of L. monocytogenes using a 26 h proprietary enrichment broth. The VIDAS LMX method was validated according to harmonized AOAC Research Institute (RI) and Official Methods of Analysis guidelines in both the AOAC Performance Tested Method (PTM) and GovVal programs. In the PTM comparison studies, the VIDAS LMX method was compared to the U.S. Department of Agriculture-Food Safety and Inspection Service Microbiology Laboratory Guidebook, the U.S. Food and Drug Administration Bacteriological Analytical Manual, and AOAC Official Methods. The comparative food studies consisted of two main parts: internal testing and AOAC independent laboratory testing, which included seven food matrixes (deli ham, processed cheese, vanilla ice cream, cooked shrimp, smoked white fish, frozen spinach, and peanut butter). As part of the AOAC R1 GovVal program, the VIDAS LMX method was compared to the Health Canada MFHPB-30 method for the detection of L. monocytogenes in five ready-to-eat (RTE) meats (hot dogs, deli turkey, deli ham, fermented sausage, and liver paté). Twenty replicates of each inoculation level and five uninoculated controls were evaluated in each study. The LMX method also included the use ofchromogenic media, chromID Ottaviani Agosti agar and chromID L. mono. agar, for confirmation of LMX presumptive results. In both the PTM and GovVal evaluations, there were no significant differences in the Chi-square values for the LMX method when compared to reference methods. The additional parameters tested in the PTM evaluation (inclusivity, exclusivity, ruggedness, stability, and lot-to-lot) satisfied the AOAC RI performance requirements. In both the PTM and GovVal validation studies, the VIDAS LMX method demonstrated reliability as a rapid qualitative method for next-day detection of L

Full Text Available Listeria monocytogenes harbouring niches established in the processing plant support post-process contamination of dairy products made from pasteurised or thermised milk. The present study investigated L. monocytogenes environmental contamination in two sheep’s milk cheese-making plants. Persistence of contamination in the area at higher risk was also investigated. During a one-year survey 7 samplings were carried out in each dairy plant, along the production lines of Pecorino Romano and ricotta salata cheese. A total of 613 environmental samples collected from food contact and non-food contact surfaces were analysed according to ISO 11290-1:2005 standard method. Identification of the isolated strains was carried out by polymerase chain reaction. L. monocytogenes prevalence was 23.2% in dairy A and 13.1% in dairy B, respectively. The higher prevalence rate was found in the following areas: salting, products washing, packaging, ricotta salata storage and Pecorino Romano ripening rooms. L. monocytogenes was never found in the cheese-making area. The probability of observing samples positive for the presence of L. monocytogenes was asso- ciated with dairy plant, sampling area and the period of cheese-making (P<0.001. The greater persistence of contamination over time was observed in the washing, salting, and Pecorino Romano ripening areas. The control of persistent environmental contamination relies on the identification of L. monocytogenes niches within the processing environment and the prevention of harborage sites formation. The importance of strict cleaning and sanitising procedure in controlling L. monocytogenes environmental contamination is confirmed by the lower level of contamination observed after these procedures were correctly implemented.

Murine infection with Listeria monocytogenes induces CD8+ T cell responses specific for bacterial peptides that are presented on the infected cell surface by MHC class Ia and MHC class Ib molecules. We have used MHC tetramers to demonstrate that CD8+ T cells restricted by the H2-M3 MHC class Ib molecules constitute a substantial portion of the T cell response to L. monocytogenes infection. The in vivo size and kinetics of MHC class Ib-restricted T cell populations suggests that they play a prominent role in bacterial clearance following primary L. monocytogenes infection.

abattoirs including poultry processing line samples, and final products were also examined for L. monocytogenes. Listeria monocytogenes was isolated in 0 . 3% to 18 . 7% of the samples collected in the different abattoirs. Epidemiological typing of 247 L. monocytogenes isolates, including serotyping, phage...... typing, pulsed-field gel electrophoresis and ribotyping revealed 62 different clones. Based upon typability and discriminatory power, DNA typing methods used were found equally suitable as epidemiological markers. Serotyping and phage typing were not found useful as epidemiological markers for poultry...

Transcription of the Listeria monocytogenes positive regulatory factor A protein (PrfA) is initiated from either of two promoters immediately upstream of prfA (prfAp1 and prfAp2) or from the upstream plcA promoter. We demonstrate that prfAp2 is a functional σB-dependent promoter and that a sigB deletion mutation affects the virulence phenotype of L. monocytogenes. Thus, the alternative sigma factor σB contributes to virulence in L. monocytogenes.

A variety of foods were examined for the incidence of Listeria monocytogenes, and the bacterial isolates were further characterized. L. monocytogenes was selected on LiCl-phenylethanol-moxalactam agar after enrichments and identified by several biochemical, mobility, and CAMP tests. L. monocytogenes was isolated from 58.8% of pork samples, 50% of chicken carcasses, 38% of turkey parts, 34% of frozen semiready foods, 24% of beef steaks, 12.2% of vegetables, 10.5% of seafoods, and 4.4% of froze...

Listeria monocytogenes is a Gram-positive, facultative anaerobic, rod-shaped bacterium that can infect and cause disease in many species. In this case report, we describe a case of L. monocytogenes infection causing sepsis in a sugar glider (Petaurus breviceps). The sugar glider consumed a varied diet consisting of human food items, including cantaloupe. A nationwide outbreak of L. monocytogenes foodborne illness associated with cantaloupes occurred simultaneously with this incident case. In this case, the bacterial strains from the outbreak and glider were genetically distinct. Although rare, veterinarians should be aware of the emergence of foodborne pathogens' ability to infect exotic animals residing in domestic environments.

Nurmi-type cultures (NTCs), derived from the fermentation of caecal contents of specifically pathogen-free (SPF) birds, have been used successfully to control salmonella colonisation in chicks. These cultures are undefined in nature and, consequently, it is difficult to obtain approval from regulatory agencies for their use as direct fed microbials (DFMs) for poultry. Progress towards the generation of effective defined probiotics requires further knowledge of the composition of these cultures. As such, species-specific, culture-independent quantification methodologies need to be developed to elucidate the concentration of specific bacterial constituents of NTCs. Quantification of specific bacterial species in such ill-defined complex cultures using conventional culturing methods is inaccurate due to low levels of sensitivity and reproducibility, in addition to slow turnaround times. Furthermore, these methods lack selectivity due to the nature of the accompanying microflora. This study describes the development of a rapid, sensitive, reliable, reproducible, and species-specific culture-independent, solution phase hybridisation PCR-ELISA procedure for the detection and quantification of Enterococcus faecalis and Pediococcus pentosaceus in NTCs. In this technique, biotin-labelled primers were designed to amplify a species-specific fragment of a marker gene of known copy number, in both species. Resulting amplicons were hybridised with a dinitrophenol (DNP)-labelled oligonucleotide probe in solution and were subsequently captured on a streptavidin-coated microtitre plate. The degree of binding was determined by the addition of IgG (anti-DNP)-horseradish peroxidase conjugate, which was subsequently visualised using a chromogenic substrate, tetramethylbenzidine. This novel quantitative method was capable of detecting E. faecalis and P. pentosaceus at levels as low as 5 CFU per PCR reaction.

Groupers (Epinephelus spp.) are economically important fish species in Southeast Asian aquaculture. Vibriosis caused by Vibro spp. is one of the severe bacterial diseases that devastate the grouper aquaculture industry. Probiotics have been reported to show the potential to enhance fish immunity and to antagonize pathogens. In our previous study, a lactic acid bacterium Pediococcus pentosaceus strain 4012 (LAB4012), isolated from cobia intestine, protects cobia from photobacteriosis after a 2-week feeding. In this study, we examined the potential of LAB4012 to be a probiotic for the orange-spotted grouper through feeding, thus to guard against vibriosis. In vitro, LAB4012 culture supernatant with low pH suppressed the growth of Vibrio anguillarum, and lactic acid in the metabolite of LAB4012 appeared to be the major factor to the growth inhibition of V. anguillarum. In vivo, the challenge test showed that the cumulative mortality of the LAB4012-fed groupers was significantly lower than that of the control fish after V. anguillarum infection. Supplementation of LAB4012 in commercial diet not only enhanced the growth rate and erythrocyte numbers of the groupers, but also regulated the gene expression of the pro-/anti-inflammatory cytokines. One day post-infection of V. anguillarum, the leukocyte numbers in the peripheral blood and the phagocytic activity of the head-kidney phagocytes in the LAB4012-fed groupers were found significantly increased, when compared with those without LAB4012-feeding. These results suggested that LAB4012 can be a dietary probiotic for groupers in modulating the immunity and protecting the groupers from V. anguillarum infection.

Full Text Available Growth of specific lactic acid bacteria in beer leads to spoiled product and economic loss for the brewing industry. Microbial growth is typically inhibited by the combined stresses found in beer (e.g., ethanol, hops, low pH, minimal nutrients; however, certain bacteria have adapted to grow in this harsh environment. Considering little is known about the mechanisms used by bacteria to grow in and spoil beer, transcriptome sequencing was performed on a variant of the beer-spoilage organism Pediococcus claussenii ATCC BAA-344(T (Pc344-358. Illumina sequencing was used to compare the transcript levels in Pc344-358 growing mid-exponentially in beer to those in nutrient-rich MRS broth. Various operons demonstrated high gene expression in beer, several of which are involved in nutrient acquisition and overcoming the inhibitory effects of hop compounds. As well, genes functioning in cell membrane modification and biosynthesis demonstrated significantly higher transcript levels in Pc344-358 growing in beer. Three plasmids had the majority of their genes showing increased transcript levels in beer, whereas the two cryptic plasmids showed slightly decreased gene expression. Follow-up analysis of plasmid copy number in both growth environments revealed similar trends, where more copies of the three non-cryptic plasmids were found in Pc344-358 growing in beer. Transcriptome sequencing also enabled the addition of several genes to the P. claussenii ATCC BAA-344(T genome annotation, some of which are putatively transcribed as non-coding RNAs. The sequencing results not only provide the first transcriptome description of a beer-spoilage organism while growing in beer, but they also highlight several targets for future exploration, including genes that may have a role in the general stress response of lactic acid bacteria.

Growth of specific lactic acid bacteria in beer leads to spoiled product and economic loss for the brewing industry. Microbial growth is typically inhibited by the combined stresses found in beer (e.g., ethanol, hops, low pH, minimal nutrients); however, certain bacteria have adapted to grow in this harsh environment. Considering little is known about the mechanisms used by bacteria to grow in and spoil beer, transcriptome sequencing was performed on a variant of the beer-spoilage organism Pediococcus claussenii ATCC BAA-344(T) (Pc344-358). Illumina sequencing was used to compare the transcript levels in Pc344-358 growing mid-exponentially in beer to those in nutrient-rich MRS broth. Various operons demonstrated high gene expression in beer, several of which are involved in nutrient acquisition and overcoming the inhibitory effects of hop compounds. As well, genes functioning in cell membrane modification and biosynthesis demonstrated significantly higher transcript levels in Pc344-358 growing in beer. Three plasmids had the majority of their genes showing increased transcript levels in beer, whereas the two cryptic plasmids showed slightly decreased gene expression. Follow-up analysis of plasmid copy number in both growth environments revealed similar trends, where more copies of the three non-cryptic plasmids were found in Pc344-358 growing in beer. Transcriptome sequencing also enabled the addition of several genes to the P. claussenii ATCC BAA-344(T) genome annotation, some of which are putatively transcribed as non-coding RNAs. The sequencing results not only provide the first transcriptome description of a beer-spoilage organism while growing in beer, but they also highlight several targets for future exploration, including genes that may have a role in the general stress response of lactic acid bacteria.

Some lactic acid bacteria can induce viscosity in wine, beer and cider by production of exopolysaccharides (EPS). A polymerase chain reaction (PCR) assay was previously described for the detection of ropy Pediococcus damnosus strains in wine [J. Appl. Microbiol. 90 (2001) 535]. The primers used in that study, PF5 and PF6, are investigated in addition to new primers which broaden the range of spoiling agents detectable by PCR. Primers PF1 and PF8 allow the amplification of DNA from ropy P. damnosus strains isolated from wine, as was observed with PF5 and PF6. In addition, PF1 and PF8, unlike PF5 and PF6, are able to generate an amplicon using template DNA from a ropy P. damnosus strain isolated from cider and a ropy Oenococcus oeni strain isolated from champagne. Two different ropy Lactobacillus species were also isolated, but their DNA was not amplified using primers PF1 and PF8. The new primers PF1 and PF8 were chosen from the sequence of gene dps, a putative glucan synthase gene, found across all the ropy P. damnosus strains isolated, from both wine or cider, and also in a ropy O. oeni strain. To our knowledge, this is the first time that an EPS-producing O. oeni strain is described. Glucan biosynthesis was assessed by agglutination tests done with Streptococcus pneumoniae type 37-specific antibodies, which specifically detect glucan-producing cells. The results show that there is a direct correlation between glucan production and detection of gene dps. Therefore, Dps is considered a candidate for the glucan synthase enzyme responsible for EPS production by ropy strains of P. damnosus and O. oeni.

Full Text Available The present investigation focuses on screening and optimization of media components to enhance glucansucrase and glucan production by Pediococcus pentosaceus CRAG3 at shake-flask and bioreactor level using Taguchi orthogonal array design. A three-level Taguchi orthogonal array layout of L27 (33 was employed, in which six variables were studied for their influence on glucansucrase and glucan production. The results showed that sucrose, K2HPO4 and Tween-80 were the most significant factors to improve glucansucrase production while the glucan production was mostly affected by sucrose, peptone and K2HPO4. The optimized medium composition for maximum glucansucrase and glucan production were: sucrose 3.5% and 5%; yeast extract 0.2% and 2.0%; beef extract 0.5% and 0.5%; peptone 3.0% and 1.0%; K2HPO4 0.2% and 0.2%, and Tween-80 1.0 and 0.1%, respectively. The optimized medium gave 10.1 U/ml and 10.2 U/ml glucansucrase activity while glucan concentrations were 56 mg/ml and 80 mg/ml in shake flask and bioreactor level, respectively which were in good agreement with predicted values (10.1 U/ml and 54.5 mg/ml. The optimized medium gave 2 fold enhancement in enzyme activity and 4 fold increase in glucan concentration as compared to non-optimized medium (4.5 U/ml and 15 mg/ml, respectively at shake flask level.

The production of pediocin PA-1, a small heat-stable bacteriocin, is associated with the presence of the 9.4-kbp plasmid pSRQ11 in Pediococcus acidilactici PAC1.0. It was shown by subcloning of pSRQ11 in Escherichia coli cloning vectors that pediocin PA-1 is produced and, most probably, secreted by E. coli cells. Deletion analysis showed that a 5.6-kbp SalI-EcoRI fragment derived from pSRQ11 is required for pediocin PA-1 production. Nucleotide sequence analysis of this 5.6-kbp fragment indicated the presence of four clustered open reading frames (pedA, pedB, pedC, and pedD). The pedA gene encodes a 62-amino-acid precursor of pediocin PA-1, as the predicted amino acid residues 19 to 62 correspond entirely to the amino acid sequence of the purified pediocin PA-1. Introduction of a mutation in pedA resulted in a complete loss of pediocin production. The pedB and pedC genes, encoding proteins of 112 and 174 amino acid residues, respectively, are located directly downstream of the pediocin structural gene. Functions could not be assigned to their gene products; mutation analysis showed that the PedB protein is not involved in pediocin PA-1 production. The mutation analysis further revealed that the fourth gene, pedD, specifying a relatively large protein of 724 amino acids, is required for pediocin PA-1 production in E. coli. The predicted pedD protein shows strong similarities to several ATP-dependent transport proteins, including the E. coli hemolysin secretion protein HlyB and the ComA protein, which is required for competence induction for genetic transformation in Streptococcus pneumoniae.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:1514784

Full Text Available We evaluated the effect of an oral administration of a plant-derived lactic acid bacterium, Pediococcus pentosaceus LP28 (LP28, on metabolic syndrome by using high fat diet-induced obese mice. The obese mice were divided into 2 groups and fed either a high fat or regular diet for 8 weeks. Each group was further divided into 3 groups, which took LP28, another plant-derived Lactobacillus plantarum SN13T (SN13T or no lactic acid bacteria (LAB. The lean control mice were fed a regular diet without inducing obesity prior to the experiment. LP28 reduced body weight gain and liver lipid contents (triglyceride and cholesterol, in mice fed a high fat diet for 8 weeks (40%, 54%, and 70% less than those of the control group without LAB, and P = 0.018, P<0.001, and P = 0.021, respectively, whereas SN13T and the heat treated LP28 at 121°C for 15 min were ineffective. Abdominal visceral fat in the high fat diet mice fed with LP28 was also lower than that without LAB by 44%, although it was not significant but borderline (P = 0.076. The sizes of the adipocytes and the lipid droplets in the livers were obviously decreased. A real-time PCR analyses showed that lipid metabolism-related genes, such as CD36 (P = 0.013, SCD1 encoding stearoyl-CoA desaturase 1 (not significant but borderline, P = 0.066, and PPARγ encoding peroxisome proliferator-activated receptor gamma (P = 0.039, were down-regulated by taking LP28 continuously, when compared with those of the control group. In conclusion, LP28 may be a useful LAB strain for the prevention and reduction of the metabolic syndrome.

Lactic acid bacteria (LAB) contamination of beer presents a continual economic threat to brewers. Interestingly, only certain isolates of LAB can grow in the hostile beer environment (e.g., as studied here, Lactobacillus brevis BSO 464 (Lb464) and a non-ropy isolate of Pediococcus claussenii ATCC BAA-344(T) (Pc344NR)), indicating that significant genetic specialization is required. The genes hitA, horA, horB, horC, and bsrA, which have been proposed to confer beer-spoiling ability to an organism, are suspected of counteracting the antimicrobial effects of hops. However, these genes are not present in the same combination (if at all) across beer-spoiling organisms. As such, we sought to investigate the extent to which these genes participate during Lb464 and Pc344NR mid-logarithmic growth in beer through reverse transcription quantitative PCR analysis. We first determined the optimal reference gene set needed for data normalization and, for each bacterium, established that two genes were needed for accurate assessment of gene expression. Following this, we found that horA expression was induced for Pc344NR, but not for Lb464, during growth in beer. Instead, horC expression was dramatically increased in Lb464 when growing in beer, whereas no change was detected for the other putative beer-spoilage-related genes. This indicates that HorC may be one of the principle mediators enabling growth of Lb464 in beer, whereas in Pc344NR, this may be attributable to HorA. These findings not only reveal that Lb464 and Pc344NR are unique in their beer-specific genetic expression profile but also indicate that a range of genetic specialization exists among beer-spoilage bacteria.

EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP

2013-07-01

Full Text Available Three strains of Pediococcus pentosaceus are each intended to improve the ensiling process at a dose of 1x108 CFU/kg fresh matter. This speciesis considered by EFSA to be suitable for the qualified presumption of safety approach to safety assessment. As the identity of the strains has been established and as no resistance to antibiotics of human and veterinary clinical significance was detected, the use of the strains in the production of silage is presumed safe for livestock species, consumers of products from animals fed the treated silage and for the environment. In the absence of evidence, these additives should be regarded as skin and eye irritants and potential skin sensitisers. Given the proteinaceous nature of the active agents, the FEEDAP Panel considers it prudent to treat these additives as respiratory sensitisers. Given the high dusting potential of the preparations tested, there is the need to take measures to minimise inhalation exposure of workers. Eight studies with laboratory-scale silos were conducted with P. pentosaceus applied at 1 x 108 CFU/kg forage. In all the studies, which lasted for at least 90 days, the effects of adding the additive to forage were compared to untreated control materials. All three strains of P. pentosaceus have the potential to improve the production of silage by reducing the pH and increasing lactic acid concentration, resulting in an increased preservation of dry matter. There was also evidence of a significant reduction in protein breakdown as shown by the change in the ratio of ammonia/total N. This was shown in easy and moderately difficult to ensile forage materials with a dry matter content ranging between 20 and 33 %.

Listeria monocytogenes is a bacterial pathogen classified into distinct serovars (SVs) based on somatic and flagellar antigens. To correlate phenotype with genetic variation, we analyzed the wall teichoic acid (WTA) glycosylation genes of SV 1/2, 3 and 7 strains, which differ in decoration of the ribitol-phosphate backbone with N-acetylglucosamine (GlcNAc) and/or rhamnose. Inactivation of lmo1080 or the dTDP-l-rhamnose biosynthesis genes rmlACBD (lmo1081-1084) resulted in loss of rhamnose, whereas disruption of lmo1079 led to GlcNAc deficiency. We found that all SV 3 and 7 strains actually originate from a SV 1/2 background, as a result of small mutations in WTA rhamnosylation and/or GlcNAcylation genes. Genetic complementation of different SV 3 and 7 isolates using intact alleles fully restored a characteristic SV 1/2 WTA carbohydrate pattern, including antisera reactions and phage adsorption. Intriguingly, phage-resistant L. monocytogenes EGDe (SV 1/2a) isolates featured the same glycosylation gene mutations and were serotyped as SV 3 or 7 respectively. Again, genetic complementation restored both carbohydrate antigens and phage susceptibility. Taken together, our data demonstrate that L. monocytogenes SV 3 and 7 originate from point mutations in glycosylation genes, and we show that phage predation represents a major driving force for serovar diversification and evolution of L. monocytogenes.

Full Text Available AbstractGreen mussel (Perna viridis and cockle shell (Anadara granosa are one of many sources of animal protein which is many cultivated in Indonesia because their price is relatively affordable. This study was conducted to identify the presence of Listeria monocytogenes in 27 samples of green mussels and 3 samples of cockle shells using real-time Polymerase Chain Reaction (real-time PCR and biochemical methods. The target gene for amplification in real-time PCR was an hlyA gene because this gene was a determinant of virulence genes that produce listeriolysin O. Primers used in this study were forward primer DG69 (GTG CCG GGT AAA AGA CCA TA and reverse primer DG74 (CGC CAC TGA GAT ACT AT and fluorescence signals indicator using SYBR Green I. The results of analysis using real-time PCR were negative Listeria monocytogenes in all samples, while using biochemical methods there was one of 30 samples contaminated by Listeria welshimeri.

The purpose of this study was to assess the action of various disinfectants used in food industry against biofilm cells of Listeria monocytogenes formed on stainless steel surfaces during 24, 72 and 120 hours. Numbers of viable biofilm cells decreased after treatment with all the tested disinfectants (iodine, biguanide, quaternary ammonium compounds, peracetic acid and sodium hypochlorite. Sodium hypochlorite was the most effective disinfectant against the biofilm cells, while biguanide and iodine were the least. Scanning electron microscopy observations demonstrated attached cells on stainless steel surfaces after treatment with all the disinfectants. These observations showed that microorganisms were not completely removed from stainless steel surfaces after treatment with the disinfectants, however, the attachment did not means the viability of remaining cells. The biofilm age in hours (24, 72 and 120 had no apparent influence on resistance of microbiological cells to the disinfectants under study. In conclusion biofilm cells of L. monocytogenes can withstand disinfectants action.

Contamination of luncheon meats by Listeria monocytogenes has resulted in outbreaks of listeriosis and major product recalls. Listeriae can survive on processing equipment such as meat slicers which serve as a potential contamination source. This study was conducted to determine (i) the dynamics of cross-contamination of L. monocytogenes from a commercial slicer and associated equipment onto sliced meat products, (ii) the influence of sample size on the efficacy of the BAX-PCR and U.S. Department of Agriculture-Food Safety and Inspection Service enrichment culture assays to detect L. monocytogenes on deli meat, and (iii) the fate of L. monocytogenes on sliced deli meats of different types during refrigerated storage. Three types of deli meats, uncured oven-roasted turkey, salami, and bologna containing sodium diacetate and potassium lactate, were tested. A five-strain mixture of L. monocytogenes was inoculated at ca.10(3) CFU onto the blade of a commercial slicer. Five consecutive meat slices were packed per package, then vacuum sealed, stored at 4 degrees C, and sampled at 1 and 30 days postslicing. Two sample sizes, 25 g and contents of the entire package of meat, were assayed. Total numbers of L. monocytogenes-positive samples, including the two sample sizes and two sampling times, were 80, 9, and 3 for turkey, salami, and bologna, respectively. A higher percentage of turkey meat samples were L. monocytogenes positive when contents of the entire package were assayed than when the 25-g sample was assayed (12.5 and 7.5%, respectively). Lower inoculum populations of ca. 10(1) or 10(2) CFU of L. monocytogenes on the slicer blade were used for an additional evaluation of oven-roasted turkey using two additional sampling times of 60 and 90 days postslicing. L. monocytogenes-positive samples were not detected until 60 days postslicing, and more positive samples were detected at 90 days than at 60 days postslicing. When BAX-PCR and enrichment culture assays were

Listeria monocytogenes, an important bacterial pathogen, is responsible for foodborne illnesses worldwide. Examination of food samples for the presence of L. monocytogenes and assessment of their pathogenicity is usually an effective strategy in the prevention of listeriosis. In the present study, we have tested 307 samples of milk and milk products from various places in Tamil Nadu, India for the presence of L. monocytogenes using ISO 11290 and U.S. Food and Drug Administration Bacteriological Analytical Manual methods. 16S rDNA sequencing and duplex polymerase chain reaction (PCR) analysis for prs and iap genes were used to identify L. monocytogenes at the species level. Fifteen of the 307 samples screen tested positive for L. monocytogenes. Molecular serotyping of the L. monocytogenes isolates by multiplex PCR revealed the predominance of the serogroups 1/2a and 4b. Fourteen of the 15 isolates contained all the virulence genes (inlA, inlB, hlyA, and plcA) screened for using multiplex PCR. Only one isolate of L. monocytogenes was negative for the plcA gene and in vitro phosphatidylinositol-phospholipase C activity. L. monocytogenes strains that belong to the serogroup 4b exhibited higher nematocidal activity against Caenorhabditis elegans than the serogroup 1/2a. Worms infected with L. monocytogenes were symptomatic with aberrant contraction of body muscles, loss of pharyngeal pumping, and decreased locomotion, which highlights the pathogenic potential of the L. monocytogenes isolates.

Veriflow® Listeria monocytogenes (LM) is a molecular based assay for the presumptive detection of Listeria monocytogenes from environmental surfaces, dairy, and ready-to-eat (RTE) food matrixes (hot dogs and deli meat). The assay utilizes a PCR detection method coupled with a rapid, visual, flow-based assay that develops in 3 min post PCR amplification and requires only 24 h of enrichment for maximum sensitivity. The Veriflow LM system eliminates the need for sample purification, gel electrophoresis, or fluorophore-based detection of target amplification, and does not require complex data analysis. This Performance Tested Method(SM) validation study demonstrated the ability of the Veriflow LM method to detect low levels of artificially inoculated L. monocytogenes in seven distinct environmental and food matrixes. In each unpaired reference comparison study, probability of detection analysis indicated no significant difference between the Veriflow LM method and the U.S. Department of Agriculture, Food Safety and Inspection Service Microbiology Laboratory Guidebook 8.08 or AOAC 993.12 reference method. Fifty strains of L. monocytogenes were detected in the inclusivity study, while 39 nonspecific organisms were undetected in the exclusivity study. The study results show that Veriflow LM is a sensitive, selective, and robust assay for the presumptive detection of L. monocytogenes sampled from environmental, dairy, or RTE (hot dogs and deli meat) food matrixes.

The detection of the human foodborne pathogen, Listeria monocytogenes, in food, environmental samples and clinical specimens associated with cases of listeriosis, a rare but high mortality-rate disease, requires distinguishing the pathogen from other Listeria species. Speciation...

The heat resistance of a strain of Listeria monocytogenes responsible for a listeriosis outbreak in hot dogs was not higher than the heat resistance of other L. monocytogenes strains when tested in tryptic soy broth and in laboratory-prepared hot dog batter. For the thermal death time experiments, the cells were grown to stationary phase or were starved in phosphate-buffered saline, pH 7, for 6 h at 30 degrees C. Starvation increased the heat resistance of L. monocytogenes in broth but not in hot dog batter. D-values in hot dog batter were higher than in broth. For the hot dog formulation used in this study, cooking the hot dog batter for 30 s at 71.1 degrees C (160 degrees F), or its equivalent using a z-value of 6 degrees C (11 degrees F), would inactivate 5 logs of L. monocytogenes.

Full Text Available Al Kassaa Imad, Khaled el Omari, Marwa Saati, Bachar Ismail and Monzer Hamze. 2016. Prevalence of Listeria monocytogenes in raw cow milk in north Lebanon. Lebanese Science Journal, 17(1: 39-45. Listeriosis, although a zoonosis, is an invasive disease that can affect newborns, pregnant women and immunocompromised adults. Clinical manifestations can be expressed by febrile gastroenteritis, invasive forms including severe sepsis, meningitis, rhombencephalitis, prenatal infections and abortions. Species of Listeria bacteria are ubiquitous and adaptable to the environment in animal and plant foods. This study aimed to determine the prevalence of Listeria monocytogenes in 100 samples of fresh cow milk collected from different areas of North Lebanon. Listeria monocytogenes was detected by using the Grand VIDAS technique (Biomérieux France. The results obtained revealed the absence of Listeria monocytogenes in all analyzed samples.

-Au and nano-Pt respectively), with Salmonella Enteritidis (Gram-negative) and Listeria monocytogenes (Gram-positive), to reveal possibilities of constructing bacteria-nanoparticle vehicles. Methods: Hydrocolloids of nano-Au or nano-Pt were added to two bacteria suspensions in the following order: nano......-Au + Salmonella Enteritidis; nano-Au + Listeria monocytogenes; nano-Pt + Salmonella Enteritidis; nano-Pt + Listeria monocytogenes. Samples were inspected by transmission electron microscope. Results: Visualization of morphological interaction between nano-Au and Salmonella Enteritidis and Listeria monocytogenes...... of Salmonella Enteritidis, nano-Pt were seen inside bacteria cells, probably bound to DNA and partly left bacterial cells. After washing and centrifugation, some of the nano-Pt-DNA complexes were observed within Salmonella Enteritidis. Conclusion: The results indicate that the bacteria could be used...

Listeria monocytogenes, a facultative intracellular pathogen, synthesizes an extracellular protease which is responsible for the maturation of phosphatidylcholine phospholipase C (lecithinase), a virulence factor involved in cell-to-cell spread. This work describes the environmental parameters

A monoclonal Listeria antibody, designated B4, was evaluated. The ability of the antibody to bind to viable bacteria belonging to Listeria spp, compared to bacteria of the same species killed by beat treatment, acid or base treatment, sanitizers, and irradiation was examined. The antibody was found...... to react with viable L. monocytogenes and L. innocua, but not with heat-killed (72 degrees C, 5 min) strains of these organisms. When L. monocytogenes and L. innocua were killed by methods other than heat treatment, it was ambiguous whether the antibody detected the organism or not. It was concluded...... that the B4 antibody has potential to be used in an immune capture step to capture live L, monocytogenes and L. innocua from foods prior to identification of L. monocytogenes by polymerase chain reaction (PCR)....

Listeria monocytogenes may persist for long periods in food processing environments. In some instances, this may be due to aggregation or biofilm formation. To investigate the mechanism controlling biofilm formation in the food-borne pathogen L. monocytogenes, we characterized LM-49, a mutant...... with enhanced ability of biofilm-formation generated via transposon Tn917 mutagenesis of L. monocytogenes 4b G. In this mutant, a Tn917 insertion has disrupted the coding region of the gene encoding a putative ATP binding cassette (ABC) transporter permease identical to Lmof2365_1771 (a putative ABC......-transporter permease) presented in the sequenced strain L. monocytogenes str. 4b F2365. This disrupted gene, denoted lm.G_1771, encoded a protein with 10 transmembrane helixes. The revertant, LM-49RE, was obtained by replacing lm.G_1771::Tn917 with lm.G_1771 via homologous recombination. We found that LM-49RE formed...

The aim of this study was to develop a predictive model simulating growth over time of the pathogenic bacterium Listeria monocytogenes in a soft blue-white cheese. The physicochemical properties in a matrix such as cheese are essential controlling factors influencing the growth of L. monocytogenes....... We developed a predictive tertiary model of the bacterial growth of L. monocytogenes as a function of temperature, pH, NaCl, and lactic acid. We measured the variations over time of the physicochemical properties in the cheese. Our predictive model was developed based on broth data produced...... production and retail conditions showed that the number of L. monocytogenes cells increases 3 to 3.5 log within the shelf life of the cheese....

The detection of the human foodborne pathogen, Listeria monocytogenes, in food, environmental samples and clinical specimens associated with cases of listeriosis, a rare but high mortality-rate disease, requires distinguishing the pathogen from other Listeria species. Speciation...

Recent listeriosis outbreaks and recalls associated with cantaloupes urge for studies to understand the mechanisms of cantaloupe contamination by Listeria monocytogenes. Postharvest practices such as washing and hydrocooling were suggested to facilitate the contamination of fresh fruits by human pat...

The heat resistance of a Listeria monocytogenes composite (serotypes 1/2a, 1/2b, and 4b) was determined in fresh broccoli florets, sweet green peppers, onions, mushrooms, and peas using an end-point procedure in polyester pouches. The heat resistance of L. monocytogenes was higher in peas (D(60 degrees C) = 1.0 min) and mushrooms (D(60 degrees C) = 0.7 min) than in other vegetables tested (D(60 degrees C) in onions = 0.2 min) and was highest when cells were subjected to starvation before the thermal death time experiments (D(60 degrees C) of starved L. monocytogenes in mushrooms = 1.6 min). The results showed that blanching can be used as an antilisterial treatment (inactivation of 5 logs of L. monocytogenes) when the cold spot of vegetables is treated for at least 10 s at 75 degrees C or instantaneously (<1 s) at temperatures above 82 degrees C.

Heating at slowly rising temperatures is suspected to enhance thermotolerance in Listeria monocytogenes and, since anaerobic environments have been shown to facilitate resuscitation of heat-injured cells of this micro-organism, concern may arise about the possibility of L. monocytogenes surviving in minimally preserved products. The effect of rapid ( > 10 degrees C min-1) and slow (0.3 and 0.6 degrees C min-1) heating on survival of L. monocytogenes in sous vide cooked beef was therefore examined at mild processing temperatures of 56 degrees, 60 degrees and 64 degrees C. No statistically significant difference (P = 0.70) was observed between the tested heating regimes. Since the average pH of beef was low (5.6), and little or no effect was observed, a pH-dependency of heat shock-induced thermotolerance in L. monocytogenes is suggested to account for this result.

The prevalence and levels of Listeria monocytogenes in retail raw foods covering most provincial capitals in China were studied with testing of 1036 samples of vegetables, edible mushrooms, raw meat...

In this study, the effects of the incorporation of some herbal teas at different concentrations into the ice cream mix on the population of Listeria monocytogenes were studied using Taguchi method. The ice cream mix samples flavored with herbal teas were prepared using green tea and sage at different concentrations. Afterward, fresh culture of L. monocytogenes was inoculated into the samples and the L. monocytogenes was counted at different storage periods. Taguchi method was used for experimental design and analysis. In addition, some physicochemical properties of samples were examined. Results suggested that there was some effect, although little, on the population of L. monocytogenes when herbal tea was incorporated into the ice cream mix. Additionally, the use of herbal tea caused a decrease in the pH values of the samples and significant changes in the color values.

Despite its prominent role as an intracellular human pathogen, Listeria monocytogenes normally features a saprophytic lifestyle, and shares many environmental habitats with predatory protozoa. Earlier studies claimed that Acanthamoeba may act as environmental reservoirs for L.?monocytogenes, wher......Despite its prominent role as an intracellular human pathogen, Listeria monocytogenes normally features a saprophytic lifestyle, and shares many environmental habitats with predatory protozoa. Earlier studies claimed that Acanthamoeba may act as environmental reservoirs for L.......?monocytogenes, whereas others failed to confirm this hypothesis. Our findings support the latter and provide clear evidence that L.?monocytogenes is unable to persist in Acanthamoeba castellanii and A.?polyphaga. Instead, external Listeria cells are rapidly immobilized on the surface of Acanthamoeba trophozoites...... that formation of backpacks is not specific for L.?monocytogenes, and independent of bacterial pathogenicity or virulence. Hence, backpacking appears to represent a unique and highly effective strategy of Acanthamoeba to trap and feed on motile bacteria....

of nisin to CO2 packed cold-smoked salmon resulted in a 1 to 2 log reduction of L. monocytogenes followed by a lag phase of 8 and 20 days in salmon with 500 and 1000 IU nisin/g, respectively. The levels of L. monocytogenes remained below 10(3) cfu/g during 27 days of storage at both concentrations of nisin...

The Amur River’s influence on the distribution of the opportunistic bacteria Listeria monocytogenes in the western part of the Sea of Okhotsk is discussed. The presence of Listeria in the seawater, sea ice, and sediments on the northeastern Sakhalin shelf and slope supports the idea of its connection with the Amur River discharge. The hypothesis of the allochtonic parentage of L. monocytogenes in the sea’s development is proved.

Full Text Available The awareness of Listeria monocytogenes as a pathogen in meningitis and bacteremia in immunosuppressed patients is high. We report a case of vascular graft infection due to Listeria monocytogenes as an example of a less well-known manifestation of listeriosis and focus on the possible treatment procedures emphasizing a management with surgical debridement but preservation of the endograft, in contrast to the gold standard treatment of vascular graft infections which consists of a removal of the graft.

Full Text Available Listeria monocytogenes, a foodborne pathogen that can cause listeriosis through the consumption of food contaminated with this pathogen. The ability of L. monocytogenes to survive in extreme conditions and cause food contaminations have become a major concern. Hence, routine microbiological food testing is necessary to prevent food contamination and outbreaks of foodborne illness. This review provides insight into the methods for cultural detection, enumeration and molecular identification of L. monocytogenes in various food samples. There are a number of enrichment and plating media that can be used for the isolation of L. monocytogenes from food samples. Enrichment media such as buffered Listeria Enrichment Broth (BLEB, Fraser broth and University of Vermont Medium (UVM Listeria enrichment broth are recommended by regulatory agencies such as FDA-BAM, USDA-FSIS and ISO. Many plating media are available for the isolation of L. monocytogenes, for instance, PALCAM, Oxford and other chromogenic media. Besides, reference methods like FDA-BAM, ISO 11290 method and USDA-FSIS method are usually applied for the cultural detection or enumeration of L. monocytogenes. MPN technique is applied for the enumeration of L. monocytogenes in the case of low level contamination. Molecular methods including polymerase chain reaction (PCR, multiplex polymerase chain reaction (mPCR, real-time/quantitative polymerase chain reaction (qPCR, nucleic acid sequence-based amplification (NASBA, loop-mediated isothermal amplification (LAMP, DNA microarray and Next Generation Sequencing (NGS technology for the detection and identification of L. monocytogenes are discussed in this review. Overall, molecular methods are rapid, sensitive, specific, time- and labour-saving. In future, there are chances for the development of new techniques for the detection and identification of foodborne with improved features.

Background The highest incidence of listeriosis, due to consumption of ready-to-eat foods and fresh, shredded, minimally processed vegetables, occurs among pregnant women and the elderly. In order to reduce the prevalence of listeriosis among consumers, better protective measures are recommended. Chitosan films, with or without added essential oils, represent a modern, safe method of preserving the quality of such vegetables and significantly reducing the incidence of Listeria monocytogenes in these foods. Objectives The present study was conducted to evaluate the antimicrobial properties of composite chitosan-gelatin films with and without essential oils against two strains of L. monocytogenes, ATCC 19115 and ATCC 19112, in fresh shredded cabbage. Methods Shredded cabbage was inoculated with L. monocytogenes and packed between two layers of the chitosan composite film, then placed in Petri dishes. The prepared samples were stored at 4°C then analyzed for total viable count on PALCAM agar while incubated at 37°C, every 24 hours for 7 days. Results Average L. monocytogenes content ranged from 4.2 - 5.4 log CFU/g, reaching values of 7.2 - 8.6 log CFU/g in samples of untreated cabbage. A complete reduction of L. monocytogenes ATCC 19115 on cabbage was achieved after 120 hours in the presence of 0.5% chitosan film, whereas reduction of L. monocytogenes ATCC 19112 was achieved after 144 hours. In the presence of 1% chitosan film, the bacteria withered more quickly and complete reduction of both species of L. monocytogenes was achieved after 96 hours. Conclusions All tested formulations of chitosan films exhibited strong antimicrobial activity on the growth of both strains of L. monocytogenes on cabbage. The best effect was achieved with a 1% chitosan concentration. The addition of essential oils increased the antimicrobial activity of all tested films. PMID:27800143

Listeria monocytogenes is a foodborne pathogen of significant concern to the agricultural and food processing industry because of its ability to grow and persist in cool and moist environments and its association with listeriosis, a disease with a very high mortality rate. Although there have been no listeriosis outbreaks attributed to fresh mushrooms in the United States, retail surveys and recalls are evidence that L. monocytogenes contamination of mushrooms (Agaricus bisporus) can occur. The objective of this study was to determine the prevalence of Listeria spp., including L. monocytogenes, in a small-scale mushroom production facility on the campus of the Pennsylvania State University in the United States. Of 184 samples taken from five production zones within the facility, 29 (15.8%) samples were positive for Listeria spp. Among the Listeria spp. isolates, L. innocua was most prevalent (10.3%) followed by L. welshimeri (3.3%), L. monocytogenes (1.6%), and L. grayi (0.5%). L. monocytogenes was recovered only from the phase I raw material composting area. Isolates of L. monocytogenes were confirmed and serotyped by multiplex PCR. The epidemiological relatedness of the three L. monocytogenes isolates to those serotypes or lineages frequently encountered in listeriosis infections was determined by multi-virulence-locus sequence typing using six virulence genes, namely, prfA, inlB, inlC, dal, clpP, and lisR. The phylogenetic positions of the three isolates in the dendrogram prepared with data from other isolates of L. monocytogenes showed that all isolates were grouped with serotype 4a, lineage IIIA. To date, this serotype has rarely been reported in foodborne disease outbreaks.

The transcriptional activator PrfA is required for the expression of virulence factors necessary for Listeria monocytogenes pathogenesis. PrfA is believed to become activated following L. monocytogenes entry into the cytosol of infected host cells resulting in the induction of target genes whose products are required for bacterial intracellular growth and cell-to-cell spread. Several mutations have been identified that appear to lock PrfA into its highly activated cytosolic form (known as prf...

The objective of this study was to evaluate the fate of Staphylococcus aureus, Listeria monocytogenes, and natural microbiota on fresh-cut tropical fruits (pitaya, mango, papaya and pineapple) with commercial PVC film at different storage temperature (5, 13, and 25 °C). The results showed that S. aureus, L. monocytogenes, and natural microbiota increased significantly on fresh-cut tropical fruits at 25 °C. Both pathogen and natural microbiota were able to grow on fresh-cut tropical fruits at 13 °C. The maximum population of L. monocytogenes was higher than that of S. aureus on fresh-cut tropical fruits. L. monocytogenes and S. aureus could survive without growth on fresh-cut pitaya, mango, and papaya at 5 °C. The population of L. monocytogenes declined significantly on fresh-cut pineapple at all temperature, indicating composition of fresh-cut pineapple could inhibit growth of L. monocytogenes. However, S. aureus was still able to grow on fresh-cut pineapple at storage temperature. Thus, this study suggests that 4 kinds of fresh-cut tropical fruits (pitaya, mango, papaya, and pineapple) should be stored at low temperature to extend shelf life as well as to ensure the safety of fresh-cut fruits. The data collected in this study demonstrated that L. monocytogenes and S. aureus were able to grow on fresh-cut tropical fruits at different temperatures. These results could be of interest in knowing the capacity of tropical fruits to support the growth of L. monocytogenes and S. aureus. This information may also be useful to local and state regulatory officials responsible for food safety.

The growth of Listeria monocytogenes in further-processed meat products has become a major concern and an important food safety issue. The meat and poultry industries have incorporated interventions such as organic acids in marinades to inhibit the growth of L. monocytogenes. In this study, organic acids were utilized in the raw product and as a postcook dip to determine their inhibitory effect on the growth of L. monocytogenes in turkey deli loaves. The turkey deli loaves were processed, cooked, cooled, inoculated with streptomycin-resistant L. monocytogenes, and then dipped. Treatments were potassium lactate (PL) in the raw product with sodium lactate (SL), sodium diacetate (SD) dip, PL with SL/PL/SD dip, SL with SL/SD dip, and SL with SL/PL/SD dip. There was also a positive (inoculated) and negative (noninoculated) control, which was dipped in distilled water. Days 0, 7, 14, 21, 28, 42, and 56 were sampled for L. monocytogenes. There were no differences (P>0.05) among the organic acid treatments in the turkey deli loaves at any time points; therefore, all of the treatments increased the lag phase of L. monocytogenes, extending the shelf-life of the product. However, there was a difference between the treatments and the positive control at d 7, 14, 21, 28, 42, and 56. The growth of L. monocytogenes increased immediately in the positive control, whereas the negative control appeared to have no growth. These organic acids can provide meat processors with a useful method for extending the lag phase of L. monocytogenes in ready-to-eat meat and poultry products.

Listeria monocytogenes can cause listeriosis, a severe foodborne disease. In Brazil, despite very few reported cases of listeriosis, the pathogen has been repeatedly isolated from dairies. This has led the government to implement specific legislation to reduce the hazard. Here, we determined the ....... monocytogenes in dairies and retail products emphasize the need for continuous surveillance of this pathogen in the Brazilian dairy industry. (C) 2017 Elsevier Ltd. All rights reserved....

The present study aimed to assess the activity of cell-free supernatant (CFS) containing bacteriocins on the formation and maintenance of biofilms developed by Listeria monocytogenes, and the associated effect of bacteriocins and ethylene-diamine-tetra-acetic acid (EDTA) on the formed biofilm. CFS from 9 lactic acid bacteria (LAB) strains was tested for inhibitory activity against 85 L. monocytogenes isolates and 21 LAB strains. Then, 12 L. monocytogenes strains were selected based on genetic profiles and sensitivity to CFS and were subjected to an in vitro assay to assess biofilm formation in microtiter plates, considering different culture media and incubation conditions. Based on these results, 6 L. monocytogenes strains were subjected to the same in vitro procedure to assess biofilm formation, being co-inoculated with CFS. In addition, these strains were subjected to the same in vitro procedure, modified by adding the CFS after biofilm formation. Relevant decrease in biofilm formation was observed in the first experiment, but CFS added after biofilm formation did not eliminate them. CFS from Lactobacillus curvatus ET31 were selected due to its anti-biofilm activity, being associated to EDTA at different concentrations and tested for biofilm control of three strains of L. monocytogenes, using the same in vitro procedure described previously. Concentrated bacteriocin presented poor performance in eliminating formed biofilms, and EDTA concentration presented no evident interference on biofilm elimination. Twelve selected L. monocytogenes strains were positive for investigated virulence makers and negative for luxS gene, recognized as being involved in biofilm formation. Selected L. monocytogenes strains were able to produce biofilms under different conditions. CFSs have the potential to prevent biofilm formation, but they were not able to destroy already formed biofilms. Nevertheless, low concentrations of CFS combined with EDTA caused a relevant reduction in

Listeria monocytogenes, a foodborne pathogen that can cause listeriosis through the consumption of food contaminated with this pathogen. The ability of L. monocytogenes to survive in extreme conditions and cause food contaminations have become a major concern. Hence, routine microbiological food testing is necessary to prevent food contamination and outbreaks of foodborne illness. This review provides insight into the methods for cultural detection, enumeration, and molecular identification of L. monocytogenes in various food samples. There are a number of enrichment and plating media that can be used for the isolation of L. monocytogenes from food samples. Enrichment media such as buffered Listeria enrichment broth, Fraser broth, and University of Vermont Medium (UVM) Listeria enrichment broth are recommended by regulatory agencies such as Food and Drug Administration-bacteriological and analytical method (FDA-BAM), US Department of Agriculture-Food and Safety (USDA-FSIS), and International Organization for Standardization (ISO). Many plating media are available for the isolation of L. monocytogenes, for instance, polymyxin acriflavin lithium-chloride ceftazidime aesculin mannitol, Oxford, and other chromogenic media. Besides, reference methods like FDA-BAM, ISO 11290 method, and USDA-FSIS method are usually applied for the cultural detection or enumeration of L. monocytogenes. most probable number technique is applied for the enumeration of L. monocytogenes in the case of low level contamination. Molecular methods including polymerase chain reaction, multiplex polymerase chain reaction, real-time/quantitative polymerase chain reaction, nucleic acid sequence-based amplification, loop-mediated isothermal amplification, DNA microarray, and next generation sequencing technology for the detection and identification of L. monocytogenes are discussed in this review. Overall, molecular methods are rapid, sensitive, specific, time- and labor-saving. In future, there are

A listeriosis outbreak, in dairy cattle, with a high case mortality and acute death after onset of symptoms was investigated using gross pathology and bacteriologic approaches, including molecular characterization of a clinical Listeria monocytogenes isolate. In a herd of 315 animals, 9 animals showed clinical symptoms consistent with listeriosis, including 3 animals that died within 2-4 days after acute onset of clinical signs, 4 animals that were euthanized, and 2 that survived. Initial EcoRI ribotyping and serotyping indicated that this outbreak was caused by an unusual L. monocytogenes serotype 4b strain, which was classified into lineage III. Further characterization of this isolate by DNA sequencing-based subtyping methods indicated that the strain responsible for this outbreak represented a unique genotype as supported by its classification into a new sigB allelic type, which has not been identified previously among >290 isolates, and by compelling phylogenetic evidence. While lineage III isolates are generally rare, they seem to be more common among L. monocytogenes isolates from animals with clinical signs of listeriosis. This is the first report of a particularly severe clinical course of disease associated with infection by a lineage III strain. The high prevalence of Listeria spp., including L. monocytogenes, in the farm environments may favor emergence and evolution of novel, and possibly more virulent, L. monocytogenes strains. Continued monitoring of animal listeriosis cases and outbreaks may not only improve animal health but also aid in the early discovery of newly emerging L. monocytogenes strains.

Full Text Available Background Listeria monocytogenes is a foodborne pathogen and a serious threat to the public health in the world. Consumption of traditional foods such as dairy and meat products can be a major reason for relative abundance and isolation of these bacteria. Objectives The purpose of this study was to determine the phenotypic and genotypic characteristics of L. monocytogenes strains isolated from dairy and meat products. Materials and Methods A total of 317 dairy products and meat-processed samples were collected. Antibiotic susceptibility test was performed on each sample by the disk diffusion method (Kirby Bauer. Five reference loci were used for typing of L. monocytogenes strains by MLVA (Multiple Locus VNTR Analysis Technique. Results A total of 24 L. monocytogenes isolates were collected from the dairy and meat products. Resistance of isolated L. monocytogenes strains to penicillin G were 54.54% (from dairy products and 46.15% (from processed meat. Genetic relatedness of isolates were assessed by MLVA. Out of 13 different types, type 2 with 6 strains and type 3 with 4 strains, were the most common types. Conclusions MLVA analysis showed that samples obtained from different sources could have similar genetic profile. As a result, administration of penicillin in patients with listeriosis (especially pregnant women and antibiotic susceptibility test are recommended. The fast and accurate methods such as MLVA for tracking of pollution sources of L. monocytogenes are recommended during outbreaks.

Listeria monocytogenes is of major significance in human and veterinary medicine. Most human Listeria infections are foodborne and the association of contaminated milk and dairy produce consumption with human listeriosis is noteworthy. In Ethiopia, there is limited data regarding the prevalence of L. monocytogenes in raw bovine milk and dairy products. The aim of this study was, therefore, to determine the prevalence of L. monocytogenes in raw bovine milk and dairy produce. A total of 443 milk and milk product samples were microbiologically analyzed following methods recommended by the U.S. Food and Drug Administration Bacteriological Analytical Manual to isolate Listeria spp. The overall prevalence of Listeria spp. was 28.4% and specifically that of L. monocytogenes was 5.6%. Taking the prevalence of Listeria spp. into consideration, cheese was found to be highly contaminated at 60%, followed by pasteurized milk samples (40%), raw milk (18.9%) and yoghurt (5%). Considering the prevalence of Listeria monocytogenes only, raw milk had the lowest contamination while cheese had the highest, followed by pasteurized milk and yoghurt. Raw milk and milk products produced in urban and peri-urban areas of central Ethiopia were contaminated with pathogenic bacteria, L. monocytogenes. The detection of this pathogen in raw milk and milk products warrants an urgent regulatory mechanism to be put in place and also the potential role of milk processing plants in the contamination of dairy products should be investigated.

Loop-mediated isothermal amplification (LAMP) was designed for detection of Listeria monocytogenes, which is an important food-borne kind of pathogenic bacteria causing human and animal disease. The primers set for the hlyA gene consist of six primers targeting eight regions on specific gene. The LAMP assay could be performed within 40 min at 65°C in a water bath. Amplification products were visualized by calcein and manganous ion and agarose gel electrophoresis. Sensitivity of the LAMP assay for detection of L. monocytogenes in pure cultures was 2.0 CFU per reaction. The LAMP assay was 100-fold higher sensitive than that of the conventional PCR assay. Taking this way, 60 chicken samples were investigated for L. monocytogenes. The accuracy of LAMP was shown to be 100% when compared to the "gold standard" culture-biotechnical, while the PCR assay failed to detect L. monocytogenes in two of the positive samples. It is shown that LAMP assay can be used as a sensitive, rapid, and simple detection tool for the detection of L. monocytogenes and will facilitate the surveillance for contamination of L. monocytogenes in food.

Full Text Available The aim of this study was to collect actual data concerning the frequency of contamination with Listeria monocytogenes of some very popular in Bulgaria raw dried cured vacuum packed sausages, produced from October 2004 till May 2008. 148 vacuum-packed samples were taken from 9 different food business operators during all seasons of the year. The samples were analyzed according to USDA method for meat foods. Ten specimens were positive for presence of Listeria monocytogenes equal to 6,75% of all tested samples. In two other raw dried cured sausages L.welshimeri and L.innocua were found, but these species are not pathogenic for consumers. In the period before the official implementation of HACCP system (01.01.2006 in Bulgaria, 52 samples were examined and 5 Listeria monocytogenes isolates were found (~10%. 2,5 years after the HACCP implementation, 96 specimens from the same meat factories were tested and 5 Listeria monocytogenes isolates (5,2% were detected. Samples taken from lots, produced in winter time were contaminated with Listeria monocytogenes more often (7 of all 10 than specimens taken during other seasons. Data were discussed through the point of view of the effectiveness of hygienic practices and HACCP system application. Also, application of ‘microbiological criterion’ set in COMMISSION REGULATION (EC No 2073/2005 for ready-to-eat foods unable to support the growth of L. monocytogenes was considered.

To construct a recombinant strain of Listeria monocytogenes for the expression of heterologous genes, homologous recombination was utilized for insertional mutation, targeting its listeriolysin O gene(hly). The gene encoding green fluorescent protein (GFP) was used as the indicator of heterologous gene expression. The gene gfp was inserted into hly downstream from its promoter and signal sequence by an overlapping extension polymerase chain reaction, and was then cloned into the shuttle plasmid pKSV7 for allelic exchange with the L. monocytogenes chromosome. Homologous recombination was achieved by growing the electro-transformed L. monocytogenes cells on chloramphenicol plates at a non-permissive temperature.Sequencing analysis indicated correct insertion of the target gene in-frame with the signal sequence. The recombinant strain expressed GFP constitutively as revealed by fluorescence microscopy. The mutant strain L. monocytogenes hly-gfp lost its hemolytic activity as visualized on the blood agar or when analyzed with the culture supernatant samples. Such insertional mutation resulted in a reduced virulence of about 2 logs less than its parent strain L. monocytogenes 10403s as shown by the 50%-lethal-dose assays in the mouse and embryonated chicken egg models. These results thus demonstrate that mutated L. monocytogenes could be a potential carrier for the expression of heterologous passenger genes or could act as an indicator organism in the food industry.

Listeria monocytogenes is considered one of the most important foodborne pathogens. The virulence-related proteins listeriolysin O (LLO) and p60 are critical factors involved in Listeria pathogenesis. In the present study, we investigated the effect of honokiol on LLO and p60 secreted from L. monocytogenes. A listeriolysin assay was used to investigate the haemolytic activities of L. monocytogenes exposed to honokiol, and the secretion of LLO and p60 was detected by immunoblot analysis. Additionally, the influence of honokiol on the transcription of LLO and p60 genes (hly and iap, respectively) was analysed by real-time reverse transcription PCR. TNF-α release assays were performed to elucidate the biological relevance of changes in LLO and p60 secretion induced by honokiol. According to the data, honokiol showed good anti-L. monocytogenes activity, with MICs of 8-16 μg ml(-1), and the secretion of LLO and p60 was decreased by honokiol. In addition, the transcription of hly and iap was inhibited by honokiol. Our results indicate that TNF-α production by RAW264.7 cells stimulated with L. monocytogenes supernatants was inhibited by honokiol. Based on these data, we propose that honokiol could be used as a promising natural compound against L. monocytogenes and its virulence factors.

Recent studies have indicated that Listeria monocytogenes formed biofilms on the surface of food processing equipment, and may survive sanitization treatments. The purpose of this study was to compare the susceptibility of L. monocytogenes grown in either a biofilm or planktonic culture when exposed to hydrogen peroxide (H(2)O(2)). Twelve strains of biofilm-forming L. monocytogenes and their planktonic counterparts were treated with various concentrations of H(2)O(2) (1, 6, and 10%), and the cell survival was then determined at 10-min exposure intervals. When grown as a biofilm, L. monocytogenes was significantly more resistant to H(2)O(2) than under planktonic culture conditions. Planktonic L. monocytogenes strains exhibited significantly different susceptibility to 1% H(2)O(2). Equally interestingly, biofilms of the 12 L. monocytogenes strains also inhibited different survival rates after being treated with 6 and 10% H(2)O(2). However, most of the biofilms recovered to a population of 2-9 log CFU/glass fiber filter (GFF) after a 24-h re-growth period. These results indicate that there was no significant correlation between the H(2)O(2) resistance of biofilm- and planktonic-cultured cells, and suggest that different mechanisms for the resistance to sanitation or disinfection underly the persistence of certain strains in food-processing environments.

Listeria monocytogenes is a bacterial pathogen which establishes intracellular parasitism in various cells, including macrophages and nonhematopoietic cells, such as hepatocytes. It has been reported that several proinflammatory cytokines have pivotal roles in innate protection against L. monocytogenes infection. We found that a proinflammatory cytokine, interleukin 22 (IL-22), was expressed by CD3(+) CD4(+) T cells at an early stage of L. monocytogenes infection in mice. To assess the influence of IL-22 on L. monocytogenes infection in hepatocytes, cells of a human hepatocellular carcinoma line, HepG2, were treated with IL-22 before L. monocytogenes infection in vitro. Gene expression analysis of the IL-22-treated HepG2 cells identified phospholipase A2 group IIA (PLA2G2A) as an upregulated antimicrobial molecule. Addition of recombinant PLA2G2A to the HepG2 culture significantly suppressed L. monocytogenes infection. Culture supernatant of the IL-22-treated HepG2 cells contained bactericidal activity against L. monocytogenes, and the activity was abrogated by a specific PLA2G2A inhibitor, demonstrating that HepG2 cells secreted PLA2G2A, which killed extracellular L. monocytogenes. Furthermore, colocalization of PLA2G2A and L. monocytogenes was detected in the IL-22-treated infected HepG2 cells, which suggests involvement of PLA2G2A in the mechanism of intracellular killing of L. monocytogenes by HepG2 cells. These results suggest that IL-22 induced at an early stage of L. monocytogenes infection enhances innate immunity against L. monocytogenes in the liver by stimulating hepatocytes to produce an antimicrobial molecule, PLA2G2A.

Listeria monocytogenes is a Gram-positive facultative intracellular pathogen that is highly resistant to lysozyme, a ubiquitous enzyme of the innate immune system that degrades cell wall peptidoglycan. Two peptidoglycan-modifying enzymes, PgdA and OatA, confer lysozyme resistance on L. monocytogenes; however, these enzymes are also conserved among lysozyme-sensitive nonpathogens. We sought to identify additional factors responsible for lysozyme resistance in L. monocytogenes. A forward geneti...

Aims: To evaluate and model the simultaneous growth of Listeria monocytogenes and spoilage micro-organisms in cold-smoked salmon.Methods and Results: Growth kinetics of L. monocytogenes, lactic acid bacteria (LAB), Enterobacteriaceae, enterococci and Photobacterium phosphoreum were determined...... in two series of challenge tests with sliced and vacuum-packed cold-smoked salmon (SVP-CSS). The product contained a high level of smoke components and at 2degreesC levels of L. monocytogenes increased...

Listeria monocytogenes is a Gram-positive facultative intracellular pathogen that is highly resistant to lysozyme, a ubiquitous enzyme of the innate immune system that degrades cell wall peptidoglycan. Two peptidoglycan-modifying enzymes, PgdA and OatA, confer lysozyme resistance on L. monocytogenes; however, these enzymes are also conserved among lysozyme-sensitive nonpathogens. We sought to identify additional factors responsible for lysozyme resistance in L. monocytogenes. A forward geneti...

High hydrostatic pressure is a new food preservation technology known for its capacity to inactivate spoilage and pathogenic microorganisms. This study investigated the damages inflicted on Listeria monocytogenes cells treated by high pressure for 10 min at 400 MPa in pH 5.6 citrate buffer. Under these conditions, no cell growth occurred after 48 h on plate count agar. Scanning electron microscopy (SEM) revealed that cellular morphology was not really affected. Measuring propidium iodide (PI) staining followed by flow cytometry demonstrated that membrane integrity was damaged in a small part of the population, although the membrane potential evaluated by oxonol fluorescence or measured by analytical methods was reduced from - 86 to - 5 mV. These results for the first time showed that such combined methods as fluorescent dyes monitored by flow cytometry and physiological activity measurements provide valuable indications on cellular viability.

for susceptibility to ceftiofur, chloramphenicol, ciprofloxacin, erythromycin, florfenicol, penicillin, spectinomycin, streptomycin, tetracycline, tiamulin, trimethoprim, and co-trimoxazole, and the disinfectants benzalkonium chloride and triclosan, by determination of minimum inhibitory concentrations (MICs). All...... isolates were resistant to ceftiofur, but susceptible to the other antibiotics. A single isolate had a MIC of 4 mg/L for ciprofloxacin. For tiamulin. the MIC values were around the breakpoint used. Most isolates had MICs for triclosan at 16 mg/L. The MICs for benzalkonium chloride formed a bimodal...... distribution, with 105 isolates having a MIC of 4 mg/L and 9 isolates MICs of 16 and 32 mg/L. This study showed that Danish isolates of L. monocytogenes have not developed or acquired resistance to antimicrobial agents used for treatment or disinfection, except for benzalkonium chloride. The MICs for triclosan...

Full Text Available Spontaneous bacterial peritonitis is a severe and life-threatening complication in patients with ascites caused by advanced liver disease. The organisms most commonly involved are coliform bacteria and third-generation cephalosporins are the empiric antibiotics of choice. This is an uncommon case of spontaneous bacterial peritonitis caused by Listeria monocytogenes in a female patient with liver cirrhosis from autoimmune hepatitis. She did not improve with ceftriaxone and her course was complicated by hepatic encephalopathy, seizures and multi-organ failure. This case emphasizes that a high index of suspicion should be maintained for timely diagnosis and treatment. Listerial peritonitis should be suspected in patients with end-stage liver disease and inadequate response to conventional antibiotics within 48–72 h. Ampicillin/sulbactam should be initiated while awaiting results of ascitic fluid or blood culture.

A 73-year-old woman with breast cancer and metastasis under chemotherapy suffered from fever, pleural effusion and pericardial effusion. Despite the administration of treatment with cefozopran and prednisolone, the patient's fever relapsed. An electrocardiogram identified a new complete atrioventricular block and an echocardiogram revealed vegetation with an unusual pseudotumoral mass in the right atrium. Blood cultures grew Listeria monocytogenes. The patient was eventually diagnosed with right-sided infective endocarditis, which improved following the six-week administration of ampicillin and gentamicin. Homemade yoghurt was suspected to be the cause of infection in this case. Listeria endocarditis is rare; however, physicians should pay more attention to preventing this fatal disease in immunocompromised patients.

A 51-year-old Caucasian woman with Listeria monocytogenes meningitis was treated and discharged after an uncomplicated course. Her medical history included immunosuppressive treatment with prednisolone and azathioprine for autoimmune hepatitis. A diagnostic work-up after the meningitis episode...... revealed that she had low levels of the IgG4 subclass. To our knowledge, this is the first case report describing a possible association between autoimmune hepatitis and the occurrence of Listeria monocytogenes meningitis, describing a possible association between Listeria monocytogenes meningitis...... and deficiency of the IgG4 subclass and finally describing a possible association between Listeria monocytogenes meningitis and immunosuppressive therapy with prednisolone and azathioprine....

Listeria (L.) monocytogenes causes orally acquired infections and is of major importance in ruminants. Little is known about L. monocytogenes transmission between farm environment and ruminants. In order to determine potential sources of infection, we investigated the distribution of L. monocytogenes genetic subtypes in a sheep farm during a listeriosis outbreak by applying four subtyping methods (MALDI-TOF-MS, MLST, MLVA and PFGE). L. monocytogenes was isolated from a lamb with septicemia and from the brainstem of three sheep with encephalitis. Samples from the farm environment were screened for the presence of L. monocytogenes during the listeriosis outbreak, four weeks and eight months after. L. monocytogenes was found only in soil and water tank swabs during the outbreak. Four weeks later, following thorough cleaning of the barn, as well as eight months later, L. monocytogenes was absent in environmental samples. All environmental and clinical L. monocytogenes isolates were found to be the same strain. Our results show that the outbreak involving two different clinical syndromes was caused by a single L. monocytogenes strain and that soil and water tanks were potential infection sources during this outbreak. However, silage cannot be completely ruled out as the bales fed prior to the outbreak were not available for analysis. Faeces samples were negative, suggesting that sheep did not act as amplification hosts contributing to environmental contamination. In conclusion, farm management appears to be a crucial factor for the limitation of a listeriosis outbreak.

One specific DNA-subtype, as determined by RAPD, of Listeria monocytogenes persisted in a fish slaughterhouse for years, even during months with no production where the plant was cleaned and kept dry. We hypothesised that tolerance to desiccation could be a factor in explaining the persistence of L...... monocytogenes in food processing environments and the purpose of the present study was to determine ability of L monocytogenes to survive desiccation on stainless steel under simulated food processing conditions. Viable counts of eight different L. monocytogenes strains exposed to different soils and relative...... humidities (RHs) during desiccation decreased significantly (p...

The high environmental adaptability of bacteria is contingent upon their ability to sense changes in their surroundings. Bacterial pathogen entry into host poses an abrupt and dramatic environmental change, during which successful pathogens gauge multiple parameters that signal host localization. The facultative human pathogen Listeria monocytogenes flourishes in soil, water and food, and in ~50 different animals, and serves as a model for intracellular infection. L. monocytogenes identifies host entry by sensing both physical (e.g., temperature) and chemical (e.g., metabolite concentrations) factors. We report here that L-glutamine, an abundant nitrogen source in host serum and cells, serves as an environmental indicator and inducer of virulence gene expression. In contrast, ammonia, which is the most abundant nitrogen source in soil and water, fully supports growth, but fails to activate virulence gene transcription. We demonstrate that induction of virulence genes only occurs when the Listerial intracellular concentration of L-glutamine crosses a certain threshold, acting as an on/off switch: off when L-glutamine concentrations are below the threshold, and fully on when the threshold is crossed. To turn on the switch, L-glutamine must be present, and the L-glutamine high affinity ABC transporter, GlnPQ, must be active. Inactivation of GlnPQ led to complete arrest of L-glutamine uptake, reduced type I interferon response in infected macrophages, dramatic reduction in expression of virulence genes, and attenuated virulence in a mouse infection model. These results may explain observations made with other pathogens correlating nitrogen metabolism and virulence, and suggest that gauging of L-glutamine as a means of ascertaining host localization may be a general mechanism. PMID:28114430

This article presents a Listeria monocytogenes growth model in milk at the farm bulk tank stage. The main objective was to judge the feasibility and value to risk assessors of introducing a complex model, including a complete thermal model, within a microbial quantitative risk assessment scheme. Predictive microbiology models are used under varying temperature conditions to predict bacterial growth. Input distributions are estimated based on data in the literature, when it is available. If not, reasonable assumptions are made for the considered context. Previously published results based on a Bayesian analysis of growth parameters are used. A Monte Carlo simulation that forecasts bacterial growth is the focus of this study. Three scenarios that take account of the variability and uncertainty of growth parameters are compared. The effect of a sophisticated thermal model taking account of continuous variations in milk temperature was tested by comparison with a simplified model where milk temperature was considered as constant. Limited multiplication of bacteria within the farm bulk tank was modeled. The two principal factors influencing bacterial growth were found to be tank thermostat regulation and bacterial population growth parameters. The dilution phenomenon due to the introduction of new milk was the main factor affecting the final bacterial concentration. The results show that a model that assumes constant environmental conditions at an average temperature should be acceptable for this process. This work may constitute a first step toward exposure assessment for L. monocytogenes in milk. In addition, this partly conceptual work provides guidelines for other risk assessments where continuous variation of a parameter needs to be taken into account.

Full Text Available The study was aimed to characterize the probiotic properties of a Pediococcus pentosaceus strain, KID7, by in vitro and in vivo studies. The strain possessed tolerance to oro-gastrointestinal transit, adherence to the Caco-2 cell line, and antimicrobial activity. KID7 exhibited bile salt hydrolase activity and cholesterol-lowering activity, in vitro. In vivo cholesterol-lowering activity of KID7 was studied using atherogenic diet-fed hypercholesterolemic mice. The experimental animals (C57BL/6J mice were divided into 4 groups viz., normal diet-fed group (NCD, atherogenic diet-fed group (HCD, atherogenic diet- and KID7-fed group (HCD-KID7, and atherogenic diet- and Lactobacillus acidophilus ATCC 43121-fed group (HCD-L.ac as positive control. Serum total cholesterol (T-CHO level was significantly decreased by 19.8% in the HCD-KID7 group (P<0.05, but not in the HCD-L.ac group compared with the HCD group. LDL cholesterol levels in both HCD-KID7 and HCD-L.ac groups were decreased by 35.5% and 38.7%, respectively, compared with HCD group (both, P<0.05. Glutamyl pyruvic transaminase (GPT level was significantly lower in the HCD-KID7 and HCD-L.ac groups compared to HCD group and was equivalent to that of the NCD group. Liver T-CHO levels in the HCD-KID7 group were reduced significantly compared with the HCD group (P<0.05 but not in the HCD-L.ac group. Analysis of expression of genes associated with lipid metabolism in liver showed that low-density lipoprotein receptor (LDLR, cholesterol-7α-hydroxylase (CYP7A1 and apolipoprotein E (APOE mRNA expression was significantly increase in the HCD-KID7 group compared to the HCD group. Furthermore, KID7 exhibited desired viability under freeze-drying and subsequent storage conditions with a combination of skim milk and galactomannan. P. pentosaceus KID7 could be a potential probiotic strain, which can be used to develop cholesterol-lowering functional food after appropriate human clinical trials.

Full Text Available Whole-transcriptome analysis was performed on beer-spoilage organisms Lactobacillus brevis BSO 464 (Lb464 and Pediococcus claussenii ATCC BAA-344T (Pc344 when grown in growth-limiting concentrations of hop extract. This was done to delineate the hops-specific component of the total transcriptional response for these bacteria when growing in beer. The transcriptome of highly hop-tolerant isolate Lb464 had fewer genes with differential expression in response to a stronger challenge (i.e., higher bitterness units of hop extract than did Pc344, highlighting the variable nature of hop-tolerance in beer-spoilage-related lactic acid bacteria. As Lb464 can grow in pressurized/gassed beer and Pc344 cannot, this indicates that the genetic and physiological response to hops alone does not dictate the overall beer-spoilage virulence of an isolate. The general response to hops in both isolates involves pathways of acid tolerance and intracellular pH homeostasis, with glutamate and citrate metabolism, and biogenic amine metabolism as additional major responses to the presence of hop extract by Lb464 and Pc344, respectively. A Pc344 chromosomal ABC transporter (PECL_1630 was more strongly expressed than the plasmid-located, hop-tolerance ABC transporter horA. PECL_1630 is suggested to be involved in import of ATP into the cell, potentially assisting the total bacterial community when facing hop stress. This transporter is found in other beer-related P. claussenii suggesting a putative species-specific beer-spoilage-related genetic marker. Lb464 and Pc344 each contain eight plasmids and transcription from almost all occurs in response to both hops and beer. However, as evident by both transcriptional analysis and plasmid variant analysis, each bacterium harbors one plasmid that is critical for responding to hops and beer stress. For both bacteria, complex transcriptional regulation and cooperation between chromosomal and plasmid-based genes occurs in response

The antimicrobial activity of acidified sodium chlorite (ASC) against Listeria monocytogenes in salmon was studied. Raw salmon (whole fish and fillets) inoculated with L. monocytogenes (10(3) CFU/cm2 or 10(4) CFU/g) were washed with ASC solution (50 ppm) for 1 min and stored at -18 degrees C for 1 month (whole salmon) or in ice for 7 days (fillets). L. monocytogenes populations were determined for whole salmon after frozen storage and for fillets on days 1, 3, 5, and 7 of storage. A wash with ASC solution followed by ASC glazing did not reduce L. monocytogenes on the skin of whole salmon during frozen storage. However, the wash resulted in an L. monocytogenes reduction of 0.5 log CFU/g for salmon fillets. The populations of L. monocytogenes in fillets increased slowly during ice storage, but the growth of these populations was retarded by ASC ice. By day 7, the populations were 0.25 log units smaller in fillets stored in ASC ice and 0.62 log units smaller in fillets that had been washed with ASC solution and stored in ASC ice than in control fillets. Treatment with ASC also reduced total plate counts (TPCs) by 0.43 log CFU/cm2 on the skin of whole salmon and by 0.31 log CFU/g in fillets. The TPCs for skin decreased during frozen storage but increased gradually for fillets stored at 5 degrees C or in ice. However, TPCs of ASC-treated samples were lower than those for controls at any point during the study. Washing with ASC solution significantly (P < 0.05) reduced TPCs on the skin of whole salmon and in fillets, as well as L. monocytogenes in fillets. The antimicrobial activity of ASC was enhanced when salmon was washed with ASC solution and stored in ASC ice.

Full Text Available Whilst mast cells participate in the immune defence against the intracellular bacterium Listeria monocytogenes, there is conflicting evidence regarding the ability of L. monocytogenes to infect mast cells. It is known that the pore-forming toxin listeriolysin (LLO is important for mast cell activation, degranulation and the release of pro-inflammatory cytokines. Mast cells, however, are a potential source of a wide range of cytokines, chemokines and other mediators including osteopontin, which contributes to the clearing of L. monocytogenes infections in vivo, although its source is unknown. We therefore aimed to resolve the controversy of mast cell infection by L. monocytogenes and investigated the extent of mediator release in response to the bacterium. In this paper we show that the infection of bone marrow-derived mast cells by L. monocytogenes is inefficient and LLO-independent. LLO, however, is required for calcium-independent mast cell degranulation as well as for the transient and selective downregulation of cell surface CD117 (c-kit on mast cells. We demonstrate that in addition to the key pro-inflammatory cytokines TNF-α and IL-6, mast cells release a wide range of other mediators in response to L. monocytogenes. Osteopontin, IL-2, IL-4, IL-13 and granulocyte macrophage colony-stimulating factor (GM-CSF, and chemokines including CCL2, CCL3, CCL4 and CCL5 are released in a MyD88-dependent manner. The wide range of mediators released by mast cells in response to L. monocytogenes may play an important role in the recruitment and activation of a variety of immune cells in vivo. The cocktail of mediators, however, is unlikely to skew the immune response to a particular effector response. We propose that mast cells provide a hitherto unreported source of osteopontin, and may provide an important role in co-ordinating the immune response during Listeria infection.

Full Text Available Background & Objective: Listeria monocytogenes has already established as an important food born pathogen which induce listeriosis in human. Use of bacteriocins to provide food safety has been increased dramatically. Nisin has a wide spectrum inhibitory effect than the other bacteriocins and inhibits food-borne pathogens such as L. monocytogenes and many other Gram-positive spoilage microorganisms. The purpose of this study was to investigate the inhibitory effect of Nisin on population of Listeria monocytogenes and the role of changes in food components on the antilisterial properties of Nisin. Materials & Methods: The minced meat and surimi samples were inoculated by 1×104 cfu/g of L. monocytogenes. Then samples exposed to Nisin at the levels of 500 or 1000 IU/g were prepared. All treatments after packaging in plastic bags were kept for 12 days at refrigerator temperature. Samples were cultured on CHROMagarTM Listeria every 2 days and the number of listeria monocytogenes was counted. Results: two different concentrations of Nisin (500 or 1000 IU/g was not able to inhibit L. monocytogenes below the acceptable level for raw food (100 cells per g in minced meat and surimi of silver carp. But the number of bacteria reduces more in fish surimi as compared to the mince meal. Also, antilisterial activity of Nisin was reduced during the storage period. Conclusion: Inhibitory property of Nisin against L. monocytogenes in surimi significantly was higher than the minced (P<0.05. So it is possible the antilisterial properties of Nisin will increase by elimination of some enzymes during processing.

Listeria monocytogenes is a foodborne pathogen that causes listeriosis, a relatively rare but life-threatening disease primarily affecting immunocompromised individuals. The aim of this study was to determine the prevalence of L. monocytogenes in the seafood processing industry in the Republic of Ireland. The occurrence of L. monocytogenes was determined by regular sampling of both food samples and processing environment swabs at eight seafood processing facilities over two calendar years. All samples were analyzed by the International Organization for Standardization 11290-1 standard method, and the isolates were characterized by PCR, pulsed-field gel electrophoresis, serotyping, and the occurrence of some genes related to survival under stress (SSI-1, Tn6188, and bcrABC). A prevalence of 2.5% in 508 samples (433 environmental swabs and 75 food samples) was found. From the isolates obtained, eight different pulsed-field gel electrophoresis profiles were identified, two occurring in more than one facility and one occurring in food and the environment. Five of the eight pulsotypes identified contained at least one of the three stress survival-related genes tested. The tolerance of the isolates to benzalkonium chloride, a representative quaternary ammonium compound, was also examined and ranged from 5.5 ± 0.5 to 8.5 ± 0.5 ppm of benzalkonium chloride. To evaluate the ability of smoked salmon to support the growth of L. monocytogenes, including the T4 widespread pulsotype that was isolated, a challenge test was performed on cold-smoked salmon obtained from two separate producers. The results showed clearly that both types of smoked salmon supported the growth of L. monocytogenes. Although occurrence of L. monocytogenes on seafood was low, this study showed that the smoked salmon used in this study can support the growth of L. monocytogenes; therefore, vigilance is required in the processing facilities to reduce the associated risk.

The objectives of this study were to evaluate the detection of Listeria monocytogenes in different ready-to-eat foods using real-time PCR (RT-PCR). Various concentrations (10(0) to 10(5) CFU/ml) of L. monocytogenes ATCC 19115 were inoculated into ham, sausage, ground meat, processed milk, cheese, and infant formula. L. monocytogenes ATCC 19115 in the samples was then enumerated on Oxford agar, and DNA was extracted from the samples before and after incubation at 36°C for 4 h. A set of primers and hybridization probe designed in this study was then used to detect the pathogen. The standard curve was then prepared by plotting cycle threshold values for each dilution versus L. monocytogenes cell counts (log CFU). The specificity of the set of primers and hybridization probe was appropriate. A 4-h incubation at 36°C before DNA extraction produced optimum standard curves in comparison to the results for a 0-h incubation. Thus, a 4-h incubation at 36°C was applied for monitoring L. monocytogenes in collected food samples. To monitor L. monocytogenes in foods, 533 samples (ham, 129; sausage, 226; ground meat, 72; processed cheese, 54; processed milk, 42; and infant formula, 10) were collected from retail markets and from the step before pasteurization in plants. Of all 533 samples, 4 samples (0.8%) showed positive signals in RT-PCR. Two samples from hams (1.6%) and two samples from sausages (0.9%) were determined to be positive for L. monocytogenes at processed meat and milk products.

Several animal models have been used to understand the molecular basis of the pathogenicity, infectious dose and strain to strain variation of Listeria monocytogenes. The greater wax worm Galleria mellonella, as an alternative model, provides some useful advantages not available with other models and has already been described as suitable for the virulence assessment of various pathogens including L. monocytogenes. The objectives of this study are: 1) confirming the usefulness of this model with a wide panel of Listeria spp. including non-pathogenic L. innocua, L. seeligeri, L. welshimeri and animal pathogen L. ivanovii; 2) assessment of virulence of several isogenic in-frame deletion mutants in virulence and stress related genes of L. monocytogenes and 3) virulence assessment of paired food and clinical isolates of L. monocytogenes from 14 major listeriosis outbreaks occurred worldwide between 1980 and 2015. Larvae injected with different concentrations of Listeria were incubated at 37°C and monitored over seven days for time needed to kill 50% of larvae (LT50) and to determine change of bacterial population in G. mellonella, 2 and 24 hours post-inoculation. Non-pathogenic members of Listeria and L. ivanovii showed significantly (P monocytogenes strains. Isogenic mutants of L. monocytogenes with the deletions in prfA, plcA, hly, actA and virR genes, also showed significantly (P monocytogenes strains related to non-invasive (gastroenteritis) outbreaks of listeriosis showed significantly (P < 0.05) lower virulence than isolates of the same serotype obtained from outbreaks with invasive symptoms. The difference, however, was dose and strain- dependent. No significant differences in virulence were observed among the serotype tested in this study. PMID:28898264

Full Text Available Listeria monocytogenes is a significant foodborne pathogen causing severe systemic infections in humans with high mortality rates. The objectives of this work were to establish a phylogenetic framework of L. monocytogenes from China and to investigate sequence diversity among different serotypes. We selected 17 L. monocytogenes strains recovered from patients and foods in China representing serotypes 1/2a, 1/2b, and 1/2c. Draft genome sequences were determined using Illumina MiSeq technique and associated protocols. Open reading frames were assigned using prokaryotic genome annotation pipeline by NCBI. Twenty-four published genomes were included for comparative genomic and phylogenetic analysis. More than 154,000 single nucleotide polymorphisms (SNPs were identified from multiple genome alignment and used to reconstruct maximum likelihood phylogenetic tree. The 41 genomes were differentiated into lineages I and II, which consisted of 4 and 11 subgroups, respectively. A clinical strain from China (SHL009 contained significant SNP differences compared to the rest genomes, whereas clinical strain SHL001 shared most recent common ancestor with strain SHL017 from food. Moreover, clinical strains SHL004 and SHL015 clustered together with two strains (08-5578 and 08-5923 recovered from an outbreak in Canada. Partial sequences of a plasmid found in the Canadian strain were also present in SHL004. We investigated the presence of various genes and gene clusters associated with virulence and subgroup-specific genes, including internalins, L. monocytogenes pathogenicity islands (LIPIs, L. monocytogenes genomic islands (LGIs, stress survival islet 1 (SSI-1, and clustered regularly interspaced short palindromic repeats (CRISPR/cas system. A novel genomic island, denoted as LGI-2 was identified. Comparative sequence analysis revealed differences among the L. monocytogenes strains related to virulence, survival abilities, and attributes against foreign genetic

Listeria monocytogenes is responsible for one of the most life-threatening food-borne infections and the leading cause of food-poisoning associated deaths in the UK. Infection may be of the unborn/newly born infant where disease may manifest as listeric abortion, stillbirth or late-onset neonatal listeriosis, while in adults, infection usually affects the central nervous system causing meningitis. Crucial to the survival of L. monocytogenes, both inside and outside the host, is its ability to acquire metals which act as cofactors for a broad range of its cellular proteins. However, L. monocytogenes must also protect itself against the innate toxicity of metals. The importance of metals in host-pathogen interactions is illustrated by the restriction of metals (including zinc and iron) in vertebrates in response to infection and the use of high levels of metals (copper and zinc) as part of the antimicrobial defences within host phagocytes. As such, L. monocytogenes is equipped with various mechanisms to tightly control its cellular metal pools and avoid metal poisoning. These include multiple DNA-binding metal-responsive transcription factors, metal-acquisition, metal-detoxification and metal-storage systems, some of which represent key L. monocytogenes virulence determinants. This review discusses current knowledge of the role of metals in L. monocytogenes infections, with a focus on the mechanisms that contribute to zinc and copper homeostasis in this organism. The requirement to precisely control cellular metal levels may impose a vulnerability to L. monocytogenes which can be exploited in antimicrobials and therapeutics.

A mixed culture of single cells of Listeria monocytogenes and the bacteriocin producing Leuconostoc carnosum 4010 showed growth inhibition of L. monocytogenes, although the intracellular pH (pHi) of L. monocytogenes followed by fluorescence ratio imaging microscopy was not affected. Furthermore, L...

Full Text Available More than 98% of reported human listeriosis cases are caused by specific serotypes within genetic lineages I and II. The genome sequence of Listeria monocytogenes lineage III strain HCC23 (serotype 4a enables whole genomic comparisons across all three L. monocytogenes lineages. Protein cluster analysis indicated that strain HCC23 has the most unique protein pairs with nonpathogenic species Listeria innocua. Orthology analysis of the genome sequences of representative strains from the three L. monocytogenes genetic lineages and L. innocua (CLIP11262 identified 319 proteins unique to nonpathogenic strains HCC23 and CLIP11262 and 58 proteins unique to pathogenic strains F2365 and EGD-e. BLAST comparison of these proteins with all the sequenced L. monocytogenes and L. innocua revealed 126 proteins unique to serotype 4a and/or L. innocua; 14 proteins were only found in pathogenic serotypes. Some of the 58 proteins unique to pathogenic strains F2365 and EGD-e were previously published and are already known to contribute to listerial virulence.

Listeria monocytogenes is a foodborne pathogen that has been associated with poultry products. This organism is ubiquitous in nature and has been found to enter poultry further processing plants on incoming raw product. Once in the plant, L. monocytogenes can become a long term persistent colonize...

Listeria monocytogenes is a food-borne pathogen of significant threat to public health. Nisin is the only bacteriocin that can be used as a food preservative. Due to its antimicrobial activity, it can be used to control Listeria monocytogenes in food; however, the antimicrobial mechanism of nisin ...

Listeria monocytogenes is a ubiquitous bacterium that may cause the foodborne illness listeriosis. Only a small amount of data about the population genetic structure of strains isolated from food is available. This study aimed to provide an accurate view of the L. monocytogenes food strain...

Internalin A (InlA) is a critical virulence factor which mediates the initiation of Listeria monocytogenes infection by the oral route in permissive hosts. The interaction of InlA with the host cell ligand E-cadherin efficiently stimulates L. monocytogenes entry into human enterocytes, but has only a limited interaction with murine cells.

In smoked fish processes, smoking is the only step that is capable of inactivating pathogens, such as Listeria monocytogenes, that contaminate the raw fish. The objectives of this study were to examine and develop a model to describe the survival of L. monocytogenes in salmon as affected by salt, s...

Listeria monocytogenes is widely distributed in the environment. The ubiquitous nature of this bacterium can result in contamination of foods. Listeriosis is a food-borne disease caused by consumption of L. monocytogenes-contaminated food. It is a public health problem of low incidence but high mort...

Introduction: Controlling Listeria monocytogenes on ready-to-eat meat and poultry products and in food processing facilities is challenging. Surveys have found that some L. monocytogenes types are more persistent in processing facilities than others, but the reason is unknown. It is possible persist...

While rain and irrigation events have been associated with an increased prevalence of foodborne pathogens in produce production environments, quantitative data are needed to determine the effects of various spatial and temporal factors on the risk of produce contamination following these events. This study was performed to quantify these effects and to determine the impact of rain and irrigation events on the detection frequency and diversity of Listeria species (including L. monocytogenes) and L. monocytogenes in produce fields. Two spinach fields, with high and low predicted risks of L. monocytogenes isolation, were sampled 24, 48, 72, and 144 to 192 h following irrigation and rain events. Predicted risk was a function of the field's proximity to water and roads. Factors were evaluated for their association with Listeria species and L. monocytogenes isolation by using generalized linear mixed models (GLMMs). In total, 1,492 (1,092 soil, 334 leaf, 14 fecal, and 52 water) samples were collected. According to the GLMM, the likelihood of Listeria species and L. monocytogenes isolation from soil samples was highest during the 24 h immediately following an event (odds ratios [ORs] of 7.7 and 25, respectively). Additionally, Listeria species and L. monocytogenes isolates associated with irrigation events showed significantly lower sigB allele type diversity than did isolates associated with precipitation events (P = monocytogenes contamination. Small changes in management practices (e.g., not irrigating fields before harvest) may therefore reduce the risk of L. monocytogenes contamination of fresh produce. PMID:26116668

. sake LKE5 caused strong sulfurous off-flavors and was rejected as a culture for biopreservation of cold-smoked salmon. A bacteriocin-producing strain of C. piscicola (A9b) initially caused a 7-day lag phase of L. monocytogenes, followed by a reduction in numbers of L. monocytogenes from 10(3) CFU...

The presence of Listeria monocytogenes in fresh produce is a growing concern because of the possibility of food-borne illness. Ionizing radiation is an effective non-thermal means of eliminating pathogenic bacteria in fresh produce; however, the effect of ionizing irradiation on the allergenic properties of the host commodities remains unknown. This study aimed (i) to determine the effective dose of gamma-irradiation in eliminating L. monocytogenes on whole cherry tomatoes and (ii) to evaluate the effect of gamma-irradiation on the allergenic properties of tomato proteins. Cherry tomatoes that were inoculated with a mixture of five L. monocytogenes strains were treated with gamma-rays from a 60Co source. A 1.25 kGy dose of gamma-irradiation was found to be sufficient to eliminate L. monocytogenes on whole cherry tomatoes. The immunoblot profile of serum samples obtained from two patients with tomato allergy revealed that gamma-irradiation did not affect the allergenicity of tomato proteins for up to 7 days after irradiation when the tomatoes were stored at 20 °C. Additionally, the m-RNA levels of β-fructofuranosidase, polygalacturonase, pectin esterase, and superoxide dismutase, the main allergenic proteins in tomato, were not affected by the applied irradiation dose. Thus, this study demonstrated that a 1.25 kGy dose of gamma-irradiation effectively eliminates L. monocytogenes on cherry tomatoes without affecting the expression of allergenic proteins in the fruits.

Full Text Available Modern consumers are interested in the use of non-chemical methods to control pathogens when heat sterilization is not an option. Such is the case with teewurst sausage, a raw spreadable sausage and a popular German commodity. Although Listeria was not found in teewurst, the optimal microbial growing conditions of teewurst coupled with the ubiquity of L. monocytogenes in nature, makes the possibility of contamination of products very possible. This pilot study was conducted to examine teewurst’s native micro-flora’s ability to suppress the outgrowth of L. monocytogenes at 10 °C using standard plate counts and PCR-DGGE. Traditional plating methods showed L. monocytogenes growth significantly decreased when in competition with the teewurst’s native micro-flora (p < 0.05. The native micro-flora of the teewurst suppressed the overall growth of L. monocytogenes by an average of two logs, under these conditions. Denaturing Gradient Gel Electrophoresis (DGGE amplicons with unique banding patterns were extracted from DGGE gel for identification. Brochothrix thermosphacta and Lactobacillus curvatus were identified as a part of the teewurst’s native micro-flora. Although the native micro-flora did not decrease L. monocytogenes to below limits of detection, it was enough of a decrease to warrant further investigation.

Full Text Available Listeria monocytogenes is a food-borne pathogen which causes mild to life threatening disease in humans. Ingestion of contaminated food delivers the pathogen to the gastrointestinal tract, where it crosses the epithelial barrier and spreads to internal organs. Type I interferons (IFN-I are produced during infection and decrease host resistance after systemic delivery of L. monocytogenes. Here we show that mice benefit from IFN-I production following infection with L. monocytogenes via the gastrointestinal route. Intragastric infection lead to increased lethality of IFN-I receptor chain 1-deficient (Ifnar1-/- animals and to higher bacterial numbers in liver and spleen. Compared to infection from the peritoneum, bacteria infecting via the intestinal tract localized more often to periportal and pericentral regions of the liver and less frequently to the margins of liver lobes. Vigorous replication of intestine-borne L. monocytogenes in the livers of Ifnar1-/- mice 48 h post infection was accompanied by the formation of large inflammatory infiltrates in this organ and massive death of surrounding hepatocytes. This was not observed in Ifnar1-/- mice after intraperitoneal infection. The inflammatory response to infection is shaped by alterations in splenic cytokine production, particularly IFNγ, which differs after intragastric versus intraperitoneal infection. Taken together, our data suggest that the adverse or beneficial role of a cytokine may vary with the route of infection and that IFN-I are not harmful when infection with L. monocytogenes occurs via the natural route.

This work evaluates the effect of acetic acid dipping on the growth of L. monocytogenes on poultry legs stored at 4 °C for eight days. Fresh inoculated chicken legs were dipped into either a 1% or 2% acetic acid solution (v/v) or distilled water (control). Changes in mesophiles, psychrotrophs, Enterobacteriaceae counts and sensorial characteristics (odor, color, texture and overall appearance) were also evaluated. The shelf life of the samples washed with acetic acid was extended by at least two days over the control samples washed with distilled water. L. monocytogenes counts before decontamination were 5.57 log UFC/g, and after treatment with 2% acetic acid (Day 0), L. monocytogenes counts were 4.47 log UFC/g. Legs washed with 2% acetic acid showed a significant (p acetic acid. This study demonstrates that while acetic acid did reduce populations of L. monocytogenes on meat, it did not completely inactivate the pathogen. The application of acetic acid may be used as an additional hurdle contributing to extend the shelf life of raw poultry and reducing populations of L. monocytogenes.

The presence of Listeria monocytogenes in fresh produce is a growing concern because of the possibility of food-borne illness. Ionizing radiation is an effective non-thermal means of eliminating pathogenic bacteria in fresh produce; however, the effect of ionizing irradiation on the allergenic properties of the host commodities remains unknown. This study aimed (i) to determine the effective dose of gamma-irradiation in eliminating L. monocytogenes on whole cherry tomatoes and (ii) to evaluate the effect of gamma-irradiation on the allergenic properties of tomato proteins. Cherry tomatoes that were inoculated with a mixture of five L. monocytogenes strains were treated with gamma-rays from a {sup 60}Co source. A 1.25 kGy dose of gamma-irradiation was found to be sufficient to eliminate L. monocytogenes on whole cherry tomatoes. The immunoblot profile of serum samples obtained from two patients with tomato allergy revealed that gamma-irradiation did not affect the allergenicity of tomato proteins for up to 7 days after irradiation when the tomatoes were stored at 20 deg. C. Additionally, the m-RNA levels of {beta}-fructofuranosidase, polygalacturonase, pectin esterase, and superoxide dismutase, the main allergenic proteins in tomato, were not affected by the applied irradiation dose. Thus, this study demonstrated that a 1.25 kGy dose of gamma-irradiation effectively eliminates L. monocytogenes on cherry tomatoes without affecting the expression of allergenic proteins in the fruits.

The presence of Listeria monocytogenes on the rind of Gorgonzola cheese is difficult to avoid. This contamination can easily occur as a consequence of handling during ripening. The aims of this study were to determine the efficiency of high-pressure processing (HPP) for inactivation of L. monocytogenes on cheese rind and to evaluate the influence of HPP treatments on sensory characteristics. Gorgonzola cheese rinds, after removal, were inoculated (about 7.0 log CFU/g) with L. monocytogenes strains previously isolated from other Gorgonzola cheeses. The inoculated cheese rinds were processed with an HPP apparatus under conditions of pressure and time ranging from 400 to 700 MPa for 1 to 15 min. Pressures higher than 600 MPa for 10 min or 700 MPa for 5 min reduced L. monocytogenes more than 99%. A reduction higher than 99.999% was achieved pressurizing cheese rinds at 700 MPa for 15 min. Lower pressure or time treatments were less effective and varied in effectiveness with the cheese sample. Changes in sensory properties possibly induced by the HPP were evaluated on four different Gorgonzola cheeses. A panel of 18 members judged the treated and untreated cheeses in a triangle test. Only one of the four pressurized cheeses was evaluated as different from the untreated sample. HPP was effective in the reduction of L. monocytogenes on Gorgonzola cheese rinds without significantly changing its sensory properties. High-pressure technology is a useful tool to improve the safety of this type of cheese.

Full Text Available Listeria monocytogenes, a foodborne pathogen causes listeriosis, a fatal disease in about 30% of cases that affects mainly immunocompromised persons. The aim of this research was to characterize L. monocytogenes pulsed-field gel electrophoresis (PFGE types isolated from meat products collected at public markets in Araguaina city, TO. Sixty samples of raw ground beef and frescal sausage were analyzed during the second half of 2008. Five out of 30 samples (16.7% of raw ground beef tested positive for L. monocytogenes, three of which were classified as serotype 1/2b and two as serotype 4b. Among the 30 samples of sausage collected, two strains of L. monocytogenes were isolated (6.7%, one of them belonging to serotype 1/2a and the other belonging to serotype 1/2b. The restriction enzymes used were ApaI and SmaI. Similarities among the strains were determined by Dice coefficient. The macro restriction profile obtained by using SmaI enzyme allowed the distribution of seven strains in two clusters, two pulsotypes and two subtypes. The result indicates that L. monocytogenes isolates, belonging to serotype 4b, 1/2a and 1/2b, are strongly correlated within the same serotype group, and in some cases among different serotypes, suggesting that they have a common source.

Listeria monocytogenes is a Gram-positive facultatively intracellular human pathogen. Due to its saprophytic lifestyle, L. monocytogenes is assumed to infect and proliferate within soil organisms such as Caenorhabditis elegans. However, little is known about the nutrient usages and metabolite fluxes in this bacterium-nematode interaction. Here, we established a nematode colonization model for L. monocytogenes and a method for the efficient separation of the pathogen from the nematodal gut. Following (15)N labelling of C. elegans and gas chromatography-mass spectrometry-based (15)N isotopologue analysis, we detected a high basal metabolic rate of the nematode, and observed a significant metabolic flux from nitrogenous compounds of the nematode to listerial proteins during proliferation of the pathogen in the worm's intestine. For comparison, we also measured the N fluxes from the gut content into listerial proteins using completely (15)N-labelled Escherichia coli OP50 as food for C. elegans. In both settings, L. monocytogenes prefers the direct incorporation of histidine, arginine and lysine over their de novo biosynthesis. Our data suggest that colonization of nematodes is a strategy of L. monocytogenes to increase its access to N-rich nutrients.

In this study, potential mechanisms underlying resistance and adaptation to benzalkonium chloride (BC) in Listeria monocytogenes were investigated. Two groups of strains were studied. The first group consisted of strains naturally sensitive to BC which could be adapted to BC. The second group consisted of naturally resistant strains. For all adapted isolates, there was a correlation between the resistance to BC and ethidium bromide, but this was not the case for the naturally resistant isolates. To investigate the role of efflux pumps in adaptation or resistance, reserpine, an efflux pump inhibitor, was added to the strains. Addition of reserpine to the sensitive and adapted strains resulted in a decrease in the MIC for BC, whereas no such decrease was observed for the resistant strains, indicating that efflux pumps played no role in the innate resistance of certain strains of L. monocytogenes to this compound. Two efflux pumps (MdrL and Lde) have been described in L. monocytogenes. Studies showed low and intermediate levels of expression of the genes encoding the efflux pumps for two selected resistant strains, H7764 and H7962, respectively. Adaptation to BC of sensitive isolates of L. monocytogenes resulted in significant increases in expression of mdrl (P < 0.05), but no such increase was observed for lde for two adapted strains of L. monocytogenes, LJH 381 (P = 0.91) and C719 (P = 0.11). This indicates that the efflux pump Mdrl is at least partly responsible for the adaptation to BC. PMID:16672496

The effects of pronase (PRN), cellulase (CEL) or DNaseI alone or combined with benzalkonium chloride (BAC) against Listeria monocytogenes-carrying biofilms were assayed. The best removal activity against L. monocytogenes-Escherichia coli biofilms was obtained using DNaseI followed by PRN and CEL. Subsequently, a modified logistic model was used to quantify the combined effects of PRN or DNaseI with BAC. A better BAC performance after PRN compared to DNaseI eradicating L. monocytogenes was observed. In E. coli the effects were the opposite. Finally, effects of DNaseI and DNaseI-BAC treatments were compared against two different L. monocytogenes-carrying biofilms. DNaseI-BAC was more effective against L. monocytogenes when co-cultured with E. coli. Nonetheless, comparing the removal effects after BAC addition, these were higher in mixed-biofilms with Pseudomonas fluorescens. However, a high number of released viable cells was observed after combined treatments. These results open new perspectives of enzymes as an anti-biofilm strategy for environmental pathogen control.

Listeria monocytogenes is a Gram-positive facultative intracellular bacterial pathogen that invades mammalian cells and escapes from membrane-bound vacuoles to replicate within the host cell cytosol. Gene products required for intracellular bacterial growth and bacterial spread to adjacent cells are regulated by a transcriptional activator known as PrfA. PrfA becomes activated following L. monocytogenes entry into host cells, however the signal that stimulates PrfA activation has not yet been defined. Here we provide evidence for L. monocytogenes secretion of a small peptide pheromone, pPplA, which enhances the escape of L. monocytogenes from host cell vacuoles and may facilitate PrfA activation. The pPplA pheromone is generated via the proteolytic processing of the PplA lipoprotein secretion signal peptide. While the PplA lipoprotein is dispensable for pathogenesis, bacteria lacking the pPplA pheromone are significantly attenuated for virulence in mice and have a reduced efficiency of bacterial escape from the vacuoles of nonprofessional phagocytic cells. Mutational activation of PrfA restores virulence and eliminates the need for pPplA-dependent signaling. Experimental evidence suggests that the pPplA peptide may help signal to L. monocytogenes its presence within the confines of the host cell vacuole, stimulating the expression of gene products that contribute to vacuole escape and facilitating PrfA activation to promote bacterial growth within the cytosol. PMID:25822753

Listeria monocytogenes, Toxoplasma gondii and Brucella spp. can infect a wide range of species, including humans. In cetaceans, meningoencephalitis has been associated with T. gondii and Brucella spp. infection, whereas to our knowledge, L. monocytogenes infection has not previously been reported. Meningoencephalitis and L. monocytogenes, T. gondii and Brucella spp. were identified by means of both direct and indirect laboratory techniques in an adult female striped dolphin Stenella coeruleoalba found stranded in January 2015 on the Ligurian Sea coast, northwestern Italy. The animal was emaciated, and histopathology disclosed severe meningoencephalitis. The nature of the inflammatory response and intra-lesional protozoa were consistent with a mixed infection by L. monocytogenes, T. gondii and Brucella spp. We believe this is an unprecedented case of infection by 3 zoonotic pathogens and also the first bacteriologically confirmed case report of neurolisteriosis in cetaceans. Cerebral toxoplasmosis and neurobrucellosis may have led to the animal's disorientation and stranding, with L. monocytogenes having likely exacerbated the coinfection leading to the demise of this dolphin.

Listeria monocytogenes can enter the food chain at virtually any point. However, food processing environments seem to be of particular importance. From an ecological point of view, food processing facilities are microbial habitats that are constantly disturbed by cleaning and sanitizing procedures. Although L. monocytogenes is considered ubiquitous in nature, it is important to recognize that not all L. monocytogenes strains appear to be equally distributed; the distribution of the organism seems to be related to certain habitats. Currently, no direct evidence exists that L. monocytogenes-associated biofilms have played a role in food contamination or foodborne outbreaks, likely because biofilm isolation and identification are not part of an outbreak investigation, or the definition of biofilm is unclear. Because L. monocytogenes is known to colonize surfaces, we suggest that contamination patterns may be studied in the context of how biofilm formation is influenced by the environment within food processing facilities. In this review, direct and indirect epidemiological and phenotypic evidence of lineage-related biofilm formation capacity to specific ecological niches will be discussed. A critical view on the development of the biofilm concept, focused on the practical implications, strengths, and weaknesses of the current definitions also is discussed. The idea that biofilm formation may be an alternative surrogate for microbial fitness is proposed. Furthermore, current research on the influence of environmental factors on biofilm formation is discussed.

Listerial keratoconjunctivitis ('silage eye') is a wide spread problem in ruminants causing economic losses to farmers and impacts negatively on animal welfare. It results from direct entry of Listeria monocytogenes into the eye, often following consumption of contaminated silage. An isolation protocol for bovine conjunctival swabbing was developed and used to sample both infected and healthy eyes bovine eyes (n=46). L. monocytogenes was only isolated from one healthy eye sample, and suggests that this organism can be present without causing disease. To initiate a study of this disease, an infection model was developed using isolated conjunctiva explants obtained from cattle eyes post slaughter. Conjunctiva were cultured and infected for 20 h with a range of L. monocytogenes isolates (n=11), including the healthy bovine eye isolate and also strains isolated from other bovine sources, such as milk or clinical infections. Two L. monocytogenes isolates (one from a healthy eye and one from a cattle abortion) were markedly less able to invade conjunctiva explants, but one of those was able to efficiently infect Caco2 cells indicating that it was fully virulent. These two isolates were also significantly more sensitive to lysozyme compared to most other isolates tested, suggesting that lysozyme resistance is an important factor when infecting bovine conjunctiva. In conclusion, we present the first bovine conjunctiva explant model for infection studies and demonstrate that clinical L. monocytogenes isolates from cases of bovine keratoconjunctivitis are able to infect these tissues.

Listeria monocytogenes is a bacteria responsible for food borne diseases (FBD). The effect of Aloe vera gel extract as a possible bacteriostatic and/or bactericidal against Listeria monocytogenes, was checked by determined the minimum inhibitory concentration (MIC), the time of minimum inhibition (TMI) and minimum bactericidal concentration (MBC) solutions extract of Aloe vera gel in different concentrations on cultures of Listeria monocytogenes ATCC 7635. We applied the agar diffusion method, using solutions of extract of Aloe vera gel at concentrations of 0 to 100% for the MIC. The TMI was determined by growth curves in trypticase soy broth with an initial inoculum of Listeria monocytogenes ATCC 7635 of 108 CFU/mL in each solution. It was determined that the MIC was 10% extract of Aloe vera gel and TMI was 5 hours at concentrations of 10%, 20% and 30% of Aloe vera, while concentrations of 50, 80, 90 and 100%, the time was 8 hours. It was found that indeed the Aloe vera gel is bacteriostatic power on Listeria monocytogenes (p < 0.001), but yet, no bactericidal effect was obtained in our study.

Listeria monocytogenes is a common constituent of the microbiological community in poultry processing plants and can be found in low numbers on raw poultry. Raw meat is the most important source of this pathogen in commercial cooking facilities. Germicidal UV light was tested as a means to kill L. monocytogenes inoculated onto broiler breast fillets. Treatments at 800 μW/ cm(2) for 5 s to 5 min of exposure were tested against inocula of 35 to 60 cells per fillet. All fillets were sampled by rinsing in enrichment broth, and surviving pathogens were quantified using most-probable-number (MPN) analysis. Five replications each with 5 fillets per treatment were analyzed to achieve 25 sample fillets per treatment. All treatment times resulted in a significant decrease in L. monocytogenes numbers compared with paired untreated controls. Treated samples retained 0.2 to 1.5 MPN L. monocytogenes per fillet, and exposure time had no significant effect on the number of surviving cells. A 5-s treatment with germicidal UV light has potential as an intervention method to limit the transfer of L. monocytogenes on raw skinless breast fillets from a slaughter plant to a cooking plant.

Full Text Available Host defense against infection can broadly be categorized into systemic immunity and cell-autonomous immunity. Systemic immunity is crucial for all multicellular organisms, increasing in importance with increasing cellular complexity of the host. The systemic immune response to Listeria monocytogenes has been studied extensively in murine models; however, the clinical applicability of these findings to the human newborn remains incompletely understood. Furthermore, the ability to control infection at the level of an individual cell, known as “cell-autonomous immunity,” appears most relevant following infection with L. monocytogenes; as the main target, the monocyte is centrally important to innate as well as adaptive systemic immunity to listeriosis. We thus suggest that the overall increased risk to suffer and die from L. monocytogenes infection in the newborn period is a direct consequence of age-dependent differences in cell-autonomous immunity of the monocyte to L. monocytogenes. We here review what is known about age-dependent differences in systemic innate and adaptive as well as cell-autonomous immunity to infection with Listeria monocytogenes.

Four mathematical models were developed and validated for simultaneous growth of mesophilic lactic acid bacteria from added cultures and Listeria monocytogenes, during chilled storage of cottage cheese with freshor cultured cream dressing. The mathematical models include the effect of temperature...... cheese to improvemodel performance. The inhibiting effect of mesophilic lactic acid bacteria from added cultures on growth of L. monocytogenes was efficiently modelled using the Jameson approach. The new models appropriately predicted the maximum population density of L. monocytogenes in cottage cheese....... The developed models were successfully validated by using 25 growth rates for L. monocytogenes, 17 growth rates for lactic acid bacteria and a total of 26 growth curves for simultaneous growth of L. monocytogenes and lactic acid bacteria in cottage cheese. These data were used in combination with bias...

For the enumeration of Listeria monocytogenes (L. monocytogenes) in food, a sensitive enumeration method has been recently developed. This method is based on a membrane filtration of the food suspension followed by transfer of the filter on a selective medium to enumerate L. monocytogenes. An evaluation of this method was performed with several categories of foods naturally contaminated with L. monocytogenes. The results obtained with this technique were compared with those obtained from the modified reference EN ISO 11290-2 method for the enumeration of L. monocytogenes in food, and are found to provide more precise results. In most cases, the filtration method enabled to examine a greater quantity of food thus greatly improving the sensitivity of the enumeration. However, it was hardly applicable to some food categories because of filtration problems and background microbiota interference.

Listeria monocytogenes is a common cause of bacterial meningitis in elderly patients and in those with impaired cellular immunity. The most common central nervous system infection caused by L. monocytogenes is acute bacterial meningitis; meningoencephalitis is uncommon and encephalitis is rare. Early diagnosis of L. monocytogenes meningitis is difficult because only 50% of cerebrospinal fluid (CSF) Gram stains are negative. L. monocytogenes is one of the few central nervous system pathogens associated with red blood cells in the CSF. When L. monocytogenes presents as encephalitis with red blood cells in the CSF, the clinical presentation mimics most closely herpes simplex virus (HSV)-1 encephalitis. Because the therapies for L. monocytogenes and HSV-1 are different, early diagnostic differentiation is clinically important. The CSF lactic acid is the best way to rapidly differentiate between these two entities; the CSF lactic acid level is elevated in L. monocytogenes but is not elevated in HSV-1 encephalitis. The case presented is an elderly man with chronic lymphocytic leukemia who presented with encephalitis. Advanced age and chronic lymphocytic leukemia predispose him to a wide variety of pathogens, but the rapidity and severity of his clinical presentation made L. monocytogenes and HSV-1 encephalitis the most likely diagnostic possibilities. The CSF Gram stain was negative, but the elevated CSF lactic acid levels with encephalitis and red blood cells in the CSF indicated L. monocytogenes as the most likely pathogen. We present a case of L. monocytogenes encephalitis mimicking HSV-1 encephalitis. While receiving ampicillin therapy, the patient remained unresponsive for more than 1 week and then suddenly regained consciousness and recovered without neurologic sequelae.

Full Text Available Listeria monocytogenes causes foodborne illnesses through consumption of ready-to-eat foods. Although 135-201annual listeriosis cases have been estimated in Japan, the details regarding the clinical isolates such as infection source, virulence level, and other genetic characteristics, are not known. In order to uncover the trends of listeriosis in Japan and use the knowledge for prevention measures to be taken, the genetic characteristics of the past human clinical isolates needs to be elucidated. For this purpose, multilocus tandem-repeat sequence analysis (MLTSA and multi-virulence-locus sequence typing (MVLST were used in this study. The clinical isolates showed a variety of genetically distant genotypes, indicating they were from sporadic cases. However, the MVLST profiles of 7 clinical isolates were identical to those of epidemic clone (EC I isolates, which have caused several serious outbreaks in other countries, suggesting the possibility that they have strong virulence potential and originated from a single outbreak. Moreover, 6 Japanese food isolates shared their genotypes with ECI isolates, indicating that there may be risks for listeriosis outbreak in Japan. This is the first investigational study on genetic characteristics of Japanese listeriosis isolates. The listeriosis cases happened in the past are presumably sporadic, but it is still possible that some isolates with strong virulence potential have caused listeriosis outbreaks, and future listeriosis risks also exist.

The ST204 subgroup of Listeria monocytogenes is among the most frequently isolated in Australia from a range of environmental niches. In this study we provide a comparative genomics analysis of food and food environment isolates from geographically diverse sources. Analysis of the ST204 genomes showed a highly conserved core genome with the majority of variation seen in mobile genetic elements such as plasmids, transposons and phage insertions. Most strains (13/15) harbored plasmids, which although varying in size contained highly conserved sequences. Interestingly 4 isolates contained a conserved plasmid of 91,396 bp. The strains examined were isolated over a period of 12 years and from different geographic locations suggesting plasmids are an important component of the genetic repertoire of this subgroup and may provide a range of stress tolerance mechanisms. In addition to this 4 phage insertion sites and 2 transposons were identified among isolates, including a novel transposon. These genetic elements were highly conserved across isolates that harbored them, and also contained a range of genetic markers linked to stress tolerance and virulence. The maintenance of conserved mobile genetic elements in the ST204 population suggests these elements may contribute to the diverse range of niches colonized by ST204 isolates. Environmental stress selection may contribute to maintaining these genetic features, which in turn may be co-selecting for virulence markers relevant to clinical infection with ST204 isolates. PMID:28066377

One hundred and thirty-three isolates of Listeria monocytogenes from deboned fresh meat, production environment, cold cuts from five meat processing plants and from one plant producing cured dried sausages, were characterized using multilocus enzyme electrophoresis. On the basis of electrophoretically demonstrable allelic variation at 21 enzyme loci, 21 electrophoretic types (ETs) were distinguished. Analysis of the genetic relationships among the 21 ETs revealed two distinct clusters: Cluster A and Cluster B. With the exception of two isolates from one plant, all isolates from deboned fresh meat belonged to Cluster B. During processing of cold cuts, however, isolates belonging to Cluster A became more frequent, and only one of the 37 isolates from cold cuts belonged to Cluster B. In contrast, six of the nine isolates from cured dried sausages had ETs in Cluster B. One clone of Cluster A, ET-6 was isolated from cold cuts in four of six plants. This is one of the ETs most frequently recovered from patients in Norway. Isolates of ET-6 were further characterized using restriction fragment length polymorphism (RFLP) analysis of chromosomal DNA. Six distinct restriction patterns were distinguished among the 44 ET-6 strains. In one plant, four different RFLP patterns could be identified. Two clone variants seemed to have colonized different areas in this plant for at least four years. However, in each of the other plants, all ET-6 isolates had the same RFLP patterns.

The bacterial pathogen Listeria monocytogenes induces internalization into mammalian cells and uses actin-based motility to spread within tissues. Listeria accomplishes this intracellular life cycle by exploiting or antagonizing several host GTPases. Internalization into human cells is mediated by the bacterial surface proteins InlA or InlB. These two modes of uptake each require a host actin polymerization pathway comprised of the GTPase Rac1, nucleation promotion factors, and the Arp2/3 complex. In addition to Rac1, InlB-mediated internalization involves inhibition of the GTPase Arf6 and participation of Dynamin and septin family GTPases. After uptake, Listeria is encased in host phagosomes. The bacterial protein GAPDH inactivates the human GTPase Rab5, thereby delaying phagosomal acquisition of antimicrobial properties. After bacterial-induced destruction of the phagosome, cytosolic Listeria uses the surface protein ActA to stimulate actin-based motility. The GTPase Dynamin 2 reduces the density of microtubules that would otherwise limit bacterial movement. Cell-to-cell spread results when motile Listeria remodel the host plasma membrane into protrusions that are engulfed by neighbouring cells. The human GTPase Cdc42, its activator Tuba, and its effector N-WASP form a complex with the potential to restrict Listeria protrusions. Bacteria overcome this restriction through two microbial factors that inhibit Cdc42-GTP or Tuba/N-WASP interaction.

ABSTRACT The promyelocytic leukemia protein (PML) is the main organizer of stress-responsive subnuclear structures called PML nuclear bodies. These structures recruit multiple interactors and modulate their abundance or their posttranslational modifications, notably by the SUMO ubiquitin-like modifiers. The involvement of PML in antiviral responses is well established. In contrast, the role of PML in bacterial infection remains poorly characterized. Here, we show that PML restricts infection by the pathogenic bacterium Listeria monocytogenes but not by Salmonella enterica serovar Typhimurium. During infection, PML undergoes oxidation-mediated multimerization, associates with the nuclear matrix, and becomes de-SUMOylated due to the pore-forming activity of the Listeria toxin listeriolysin O (LLO). These events trigger an antibacterial response that is not observed during in vitro infection by an LLO-defective Listeria mutant, but which can be phenocopied by specific induction of PML de-SUMOylation. Using transcriptomic and proteomic microarrays, we also characterized a network of immunity genes and cytokines, which are regulated by PML in response to Listeria infection but independently from the listeriolysin O toxin. Our study thus highlights two mechanistically distinct complementary roles of PML in host responses against bacterial infection. PMID:28074026

The ST204 subgroup of Listeria monocytogenes is among the most frequently isolated in Australia from a range of environmental niches. In this study we provide a comparative genomics analysis of food and food environment isolates from geographically diverse sources. Analysis of the ST204 genomes showed a highly conserved core genome with the majority of variation seen in mobile genetic elements such as plasmids, transposons and phage insertions. Most strains (13/15) harbored plasmids, which although varying in size contained highly conserved sequences. Interestingly 4 isolates contained a conserved plasmid of 91,396 bp. The strains examined were isolated over a period of 12 years and from different geographic locations suggesting plasmids are an important component of the genetic repertoire of this subgroup and may provide a range of stress tolerance mechanisms. In addition to this 4 phage insertion sites and 2 transposons were identified among isolates, including a novel transposon. These genetic elements were highly conserved across isolates that harbored them, and also contained a range of genetic markers linked to stress tolerance and virulence. The maintenance of conserved mobile genetic elements in the ST204 population suggests these elements may contribute to the diverse range of niches colonized by ST204 isolates. Environmental stress selection may contribute to maintaining these genetic features, which in turn may be co-selecting for virulence markers relevant to clinical infection with ST204 isolates.

The relationship between the number of ingested Listeria monocytogenes cells in food and the likelihood of developing listeriosis is not well understood. Data from an outbreak of listeriosis linked to milkshakes made from ice cream produced in 1 factory showed that contaminated products were distributed widely to the public without any reported cases, except for 4 cases of severe illness in persons who were highly susceptible. The ingestion of high doses of L. monocytogenes by these patients infected through milkshakes was unlikely if possible additional contamination associated with the preparation of the milkshake is ruled out. This outbreak illustrated that the vast majority of the population did not become ill after ingesting a low level of L. monocytogenes but raises the question of listeriosis cases in highly susceptible persons after distribution of low-level contaminated products that did not support the growth of this pathogen.

Full Text Available The purpose of this study was to examine the effectiveness of selected essential oils for the control of the growth and survival of pathogenic bacteria Listeria monocytogenes ATCC 19112 and Listeria monocytogenes ATCC 19115, which are of significant importance in food hygiene. Essential oils extracted from Salvia officinalis L., Rosmarinus officinalis L., Majorana hortensis Moench., Thymus vulgaris L., Carum carvi L., Pimpinella anisum L. and Coriandrum sativum L. were evaluated. Antibacterial activity was done by the disk diffusion method in the presence of pure essential oils and four suspensions in alcohol. The best results obtained with Thymus vulgaris and Majorana hortensis essential oils, which were acting microbicidaly on both observed strains of Listeria monocytogenes, even in the small concentration. Because some of the essential oils were highly inhibitory even in small quantities to selected pathogenic bacteria, they may provide alternatives to conventional antimicrobial additives in foods. .

Listeria monocytogenes is a ubiquitous opportunistic pathogen responsible for listeriosis. In order to study the processes underlying its ability to adapt to the soil environment, whole-genome arrays were used to analyse transcriptome modifications 15 minutes, 30 minutes and 18 h after inoculation of L. monocytogenes EGD-e in soil extracts. Growth was observed within the first day of incubation and large numbers were still detected in soil extract and soil microcosms one year after the start of the experiment. Major transcriptional reprofiling was observed. Nutrient acquisition mechanisms (phosphoenolpyruvate-dependent phosphotransferase systems and ABC transporters) and enzymes involved in catabolism of specific carbohydrates (β-glucosidases; chitinases) were prevalent. This is consistent with the overrepresentation of the CodY regulon that suggests that in a nutrient depleted environment, L. monocytogenes recruits its extensive repertoire of transporters to acquire a range of substrates for energy production. PMID:21966375

In the last years, consequently to EC Regulation no. 1924/2006 on nutrition and health claims made on foods, some Italian food businnes operators (FBOs) leaders in the meat sector, invested in research to develop innovative products such as low fat salami, containing up to 30% less fat than the traditional one. For FBOs it is essential to demonstrate for each production process whether the substrate allows the growth of L. monocytogenes and whether L. monocytogenes could reach or exceed the limit of 100 cfu g–1 at the end of the shelf life, as stated by EC Regulation no. 2073/2005. In the present study, the growth potential of L. monocytogenes during the shelf life of low fat salami packed in modified atmosphere was evaluated. The results show that the product is unable to support the growth of pathogen, even if the storage temperature is between 8 and 12°C. PMID:27800321

Full Text Available Autoclaved distilled water samples were inoculated with L. monocytogenes strain V7 and strain VPH-1, and incubated aerobically, at 30 C for 48 hours. Each strain was tested individually, and growth curves were determined at 1, 2, 3, 4, 5, 21, 24, and 48 hours. The growth or survival of L. monocytogenes was similar for both strains, with survivors at 24 hour-incubation. The microbicidal activity of one synthetic cationic peptide (NP-2 was examined against L. monocytogenes strain V7, in a water system. Antibacterial activity of NP-2 (1, 5, and 10 g/ml was best expressed at 60 minute-incubation, with 10 g/ml of peptide, at 30 C.

The monitoring of a HACCP (Hazard Analysis Critical Control Point) plan for the Listeria monocytogenes control in the cooked and frozen meat section of a thermo-processing meat plant was evaluated. Seventy "non-product-contact" surface samples and fourteen finished product samples were examined. Thirty eight positive sites for the presence of Listeria sp. were obtained. Twenty-two isolates were identified as L. monocytogenes, two as L. seeligeri and fourteen as L. innocua. Non isolates were obtained from finished product samples. The detection of L. monocytogenes in cooked and frozen meat section environment showed the need for the HACCP plan to eliminate or prevent product contamination in the post-thermal step.

Full Text Available The isolation and identification of Listeria monocytogenes in processed meat samples by a combined cultural-molecular method is described. It allows the identification of Listeria strains by means of a hybridization technique with a specific DNA probe directed to the listerial internalin gene. The specificity of this method was found to be 100% and sensitivity was as low as 1 CFU/2.5 g of food sample. A total of 278 meat samples were tested in comparison with PCR and conventional cultural assays. A total of 42 (15.4% L. monocytogenes were detected. PCR analysis gave 3 false negative results and culture failed to detect the Listeria in 5 cases. With this cultural-molecular method the identification and quantitative detection of L. monocytogenes were achieved within 36 hours and no false positive or negative tests were obtained, thus fitting most food industry requirements.

Full Text Available An experimental study for the evaluation of Listeria monocytogenes inactivation during a hot smoking process in tench was performed using Listeria innocua strains. Furthermore, the survival of L. monocytogenes in smoked tench was determined after post-processing in contaminated samples, evaluating the growth potential during storage. L. innocua was not detected after the smoking process. In the challenge test, the growth potential of L. monocytogenes was 5.68 log colony forming unit g−1. The results showed that hot smoking at an inner temperature around 72°C is able to eliminate the microorganism. Nevertheless, the product is able to support the growth of the pathogen if post-process contamination occurs, as the food is suitable for Listeria multiplication. Product recontamination should be prevented by means of appropriate application of hygiene measures.

Listeria monocytogenes is an intracellular pathogen that lyses the phagosomal vacuole of infected cells, proliferates in the host cell cytoplasm and can actively enter adjacent cells. The pathogen is therefore well suited to exploitation as a vector for the delivery of DNA to target cells as the lifecycle favors cellular targeting with vector amplification and the potential for cell-to-cell spread. We have recently demonstrated DNA transfer by L. monocytogenes in growing tumors in murine models. Our approach exploited an ampicillin sensitive stain of L. monocytogenes which can be lysed through systemic administration of ampicillin to facilitate release of plasmid DNA for expression by infected mammalian cells. Here, we discuss the implications of this technology and the potential for future improvements of the system.

The antimicrobial activity of the bacteriocin-like substance (BLS) P34 against Listeria monocytogenes was investigated in chicken sausage. The BLS was applied to chicken sausages (256 AU g−1) previously inoculated with a suspension of 102 cfu g−1 of L. monocytogenes. BLS P34 inhibited the indicator microorganism in situ in all incubation times for up to 10 days at 5 °C. The effectiveness of BLS P34 was increased when it was added in combination with nisin. The bacteriocin was also tested in natural eatable natural bovine wrapping (salty semi-dried tripe) against the same indicator microorganism, also showing inhibitory capability in vitro. BLS P34 showed potential to control L. monocytogenes in refrigerated meat products. PMID:24688506

This study investigated the growth situation of Listeria monocytogenes on chilled pork and the effect of herbal preservatives on this pathogen.The inhibitions of herbal preservatives were identified. The minimum inhibitory concentrations (MIC) of cinnamon and clove were all 0.79 mg·mL-1,while the rosemary was 1.58 mg.mL-1.And the composite herbal preservatives were got through orthogonal experiment.The optimum proportion was as following on agar medium:1.16 mg·mL-1 cinnamon+2.38 mg·mL-1 rosemary+3.17mg·mL-1 clove (herb combination number 5),while on chilled pork,the strong inhibition of L.monocytogenes was showed,which demonstrated that the surface application of herb combination resulted in an effective delay of L.monocytogenes growth.

Environmental pathogens – organisms that survive in the outside environment but maintain the capacity to cause disease in mammals – navigate the challenges of life in habitats that range from water and soil to the cytosol of host cells. The bacterium Listeria monocytogenes has served for decades as a model organism for studies of host–pathogen interactions and for fundamental paradigms of cell biology. This ubiquitous saprophy te has recently become a model for understanding how an environmental bacterium switches to life within human cells. This review describes how L. monocytogenes balances life in disparate environments with the help of a critical virulence regulator known as PrfA. Understanding L. monocytogenes survival strategies is important for gaining insight into how environmental microbes become pathogens. PMID:22827306

Listeria monocytogenes has been the most common microbial cause of cheese-related recalls in both the United States and Canada in recent years. Since L. monocytogenes is inactivated by pasteurization, the majority of these cases have been linked to environmental and cross-contamination of fresh-soft, soft-ripened, and semi-soft cheeses. Cross-contamination of foods with L. monocytogenes is a continuous risk throughout the food supply chain and presents unique challenges for subsequent illness and outbreak investigations. Reports on outbreaks of listeriosis attributed to cross-contamination downstream from primary processing help highlight the critical role of epidemiological investigation coupled with coordinated molecular subtyping and surveillance in the recognition and investigation of complex foodborne outbreaks. Despite their complexity, environmental sampling throughout the supply chain coupled with improved genotyping approaches and concomitant analysis of foodborne illness epidemiological exposure data are needed to help resolve these and similar cases more rapidly and with greater confidence.

Full Text Available The antimicrobial activity of the bacteriocin-like substance (BLS P34 against Listeria monocytogenes was investigated in chicken sausage. The BLS was applied to chicken sausages (256 AU g-1 previously inoculated with a suspension of 10² cfu g-1 of L. monocytogenes. BLS P34 inhibited the indicator microorganism in situ in all incubation times for up to 10 days at 5 °C. The effectiveness of BLS P34 was increased when it was added in combination with nisin. The bacteriocin was also tested in natural eatable natural bovine wrapping (salty semi-dried tripe against the same indicator microorganism, also showing inhibitory capability in vitro. BLS P34 showed potential to control L. monocytogenes in refrigerated meat products.

Full Text Available The purpose of this research was to determine whether the cream cheese and cream that are produced in the traditional manner at home and are free to sale on Zagreb markets, meet microbiological requirements for foodstuffs (OG 46/94, 20/01, 40/01. Particular attention is given to research of bacteria Listeria monocytogenes presence in these foods, because of its exceptional hazards to human health. It was found that a majority of 64 (53 % from a total of 120 studied dairy products samples were contaminated with microbial pathogens, of which 16 % are waste in the cream cheese, and 37 % in cream samples. 39 samples of cheese and 50 samples of cream did not fulfil the conditions prescribed by the Croatian Guidelines, primarily due to the contamination with yeasts and moulds. In 10 cheese and cream samples where L. monocytogenes is proven by classical microbiological methods, PCR method confirmed L. monocytogenes in only one cream sample.

Understanding the ecology of pathogenic organisms is important in order to monitor their transmission in the environment and the related health hazards. We investigated the relationship between soil microbial diversity and the barrier effect against Listeria monocytogenes invasion. By using a dilution-to-extinction approach, we analysed the consequence of eroding microbial diversity on L. monocytogenes population dynamics under standardised conditions of abiotic parameters and microbial abundance in soil microcosms. We demonstrated that highly diverse soil microbial communities act as a biological barrier against L. monocytogenes invasion and that phylogenetic composition of the community also has to be considered. This suggests that erosion of diversity may have damaging effects regarding circulation of pathogenic microorganisms in the environment.

The antimicrobial activity of the bacteriocin-like substance (BLS) P34 against Listeria monocytogenes was investigated in chicken sausage. The BLS was applied to chicken sausages (256 AU g(-1)) previously inoculated with a suspension of 10(2) cfu g(-1) of L. monocytogenes. BLS P34 inhibited the indicator microorganism in situ in all incubation times for up to 10 days at 5 °C. The effectiveness of BLS P34 was increased when it was added in combination with nisin. The bacteriocin was also tested in natural eatable natural bovine wrapping (salty semi-dried tripe) against the same indicator microorganism, also showing inhibitory capability in vitro. BLS P34 showed potential to control L. monocytogenes in refrigerated meat products.

Full Text Available In the last years, consequently to EC Regulation no. 1924/2006 on nutrition and health claims made on foods, some Italian food businnes operators (FBOs leaders in the meat sector, invested in research to develop innovative products such as low fat salami, containing up to 30% less fat than the traditional one. For FBOs it is essential to demonstrate for each production process whether the substrate allows the growth of L. monocytogenes and whether L. monocytogenes could reach or exceed the limit of 100 cfu g–1 at the end of the shelf life, as stated by EC Regulation no. 2073/2005. In the present study, the growth potential of L. monocytogenes during the shelf life of low fat salami packed in modified atmosphere was evaluated. The results show that the product is unable to support the growth of pathogen, even if the storage temperature is between 8 and 12°C.

In the last years, consequently to EC Regulation no. 1924/2006 on nutrition and health claims made on foods, some Italian food businnes operators (FBOs) leaders in the meat sector, invested in research to develop innovative products such as low fat salami, containing up to 30% less fat than the traditional one. For FBOs it is essential to demonstrate for each production process whether the substrate allows the growth of L. monocytogenes and whether L. monocytogenes could reach or exceed the limit of 100 cfu g(-1) at the end of the shelf life, as stated by EC Regulation no. 2073/2005. In the present study, the growth potential of L. monocytogenes during the shelf life of low fat salami packed in modified atmosphere was evaluated. The results show that the product is unable to support the growth of pathogen, even if the storage temperature is between 8 and 12°C.

Full Text Available This study was conducted to evaluate the antibacterial effect of Carum copticum essential oil (Ajowan EO against Listeria monocytogenes in fish model system. Ajowan EO chemical composition was determined by gas chromatography/mass spectral analysis and the highest concentration of Carum copticum essential oil without any significant changes on sensory properties of kutum fish (Rutilus frisii kutum was assigned. Then the inhibitory effect of Ajowan EO at different concentrations in presence of salt and smoke component was tested on L. monocytogenes growth in fish peptone broth (FPB, kutum broth and cold smoked kutum broth at 4 ºC for 12 days. Ajowan EO completely decreased the number of L. monocytogenes in FPB after 12 days of storage, however, antimicrobial effect of EO significantly reduced in kutum and cold smoked kutum broth. Addition of 4% NaCl and smoke component improved the anti-listerial activity of Ajowan EO in all fish model broths.

This study was conducted to evaluate the antibacterial effect of Carum copticum essential oil (Ajowan EO) against Listeria monocytogenes in fish model system. Ajowan EO chemical composition was determined by gas chromatography/mass spectral analysis and the highest concentration of Carum copticum essential oil without any significant changes on sensory properties of kutum fish (Rutilus frisii kutum) was assigned. Then the inhibitory effect of Ajowan EO at different concentrations in presence of salt and smoke component was tested on L. monocytogenes growth in fish peptone broth (FPB), kutum broth and cold smoked kutum broth at 4 °C for 12 days. Ajowan EO completely decreased the number of L. monocytogenes in FPB after 12 days of storage, however, antimicrobial effect of EO significantly reduced in kutum and cold smoked kutum broth. Addition of 4% NaCl and smoke component improved the anti-listerial activity of Ajowan EO in all fish model broths.

Listeria monocytogenes is a gram-positive, facultative intracellular bacterium implicated in severe food-borne illness (listeriosis) in humans. The construction of well-defined gene replacements in the genome of L. monocytogenes has been instrumental to several genetic studies of the virulence and other attributes of the organism. Construction of such mutations by currently available procedures, however, tends to be labor intensive, and gene replacement mutants are sometimes difficult to recover due to lack of direct selection for the construct. In this study we describe the construction and use of plasmid vector pGF-EM, which can be conjugatively transferred from Escherichia coli S17-1 to L. monocytogenes and which provides the genetic means for direct selection of gene replacements.

This study measured and compared the short-term efficacy levels of lauric arginate (LAE) as a postlethality treatment against Listeria monocytogenes present on varied surfaces of large-diameter hams. Preliminary in vitro work demonstrated a 5-log inactivation of L. monocytogenes in 5,000- and 9,090-ppm LAE solutions within 180 min at 4.4 and 23 degrees C. Six different whole-muscle ham types were inoculated with L. monocytogenes at ca. 7-log CFU per ham and spray treated with between 15 and 29 ml of a 9,090-ppm LAE solution, or an equal volume of water (control), prior to vacuum packaging. After 48 h at 4.4 degrees C, populations were recovered from ham and interior packaging surfaces by using a surface rinse method with Dey-Engley neutralizing broth followed by plating on modified Oxford medium. Logarithmic reductions of L. monocytogenes exceeding 2 log CFU/cm(2) of ham surfaces were achieved by LAE treatment on all ham types. Hams with 1,129 cm(2) of surface area that had been processed by drenching in liquid smoke had 3.84 and 2.67 CFU/cm(2) 48 h following treatment with 18 ml of water or LAE, respectively, but increasing treatment volumes to 22 ml significantly reduced (P < 0.05) L. monocytogenes levels to 0.65 log CFU/cm(2). This study demonstrated the efficacy of LAE against L. monocytogenes on several ham types, thereby validating it as a postlethality treatment for inactivation of the pathogen.

The antimicrobial activities of oriental mustard extract alone or combined with malic acid and EDTA were investigated against Salmonella spp. or Listeria monocytogenes at different temperatures. Five strain Salmonella or L. monocytogenes cocktails were separately inoculated in Brain Heart Infusion broth containing 0.5% (w/v) aqueous oriental mustard extract and incubated at 4 °C to 21 °C for 21 d. For inhibitor combination tests, Salmonella Typhimurium 02:8423 and L. monocytogenes 2-243 were individually inoculated in Mueller Hinton broth containing the mustard extract with either or both 0.2% (w/v) malic acid and 0.2% (w/v) EDTA and incubated at 10 °C or 21 °C for 10 to 14 d. Mustard extract inhibited growth of the L. monocytogenes cocktail at 4 °C up to 21 d (2.3 log10 CFU/mL inhibition) or at 10 °C for 7 d (2.4 log10 CFU/mL inhibition). Salmonella spp. viability was slightly, but significantly reduced by mustard extract at 4 °C by 21 d. Although hydrolysis of sinigrin in mustard extract by both pathogens was 2 to 6 times higher at 21 °C than at 4 °C to 10 °C, mustard was not inhibitory at 21 °C, perhaps because of the instability of its hydrolysis product (allyl isothiocyanate). At 21 °C, additive inhibitory effects of mustard extract with EDTA or malic acid led to undetectable levels of S. Typhimurium and L. monocytogenes by 7 d and 10 d, respectively. At 10 °C, S. Typhimurium was similarly susceptible, but combinations of antimicrobials were not more inhibitory to L. monocytogenes than the individual agents.

Listeria monocytogenes is frequently found as a contaminant in raw and ready-to-eat foods. The ability of L. monocytogenes to multiply at refrigeration temperatures and to grow in a wide range of pH values is of particular concern for food safety. According to the European Union regulation on microbiological criteria for foodstuffs, L. monocytogenes must be absent in some categories of ready-to-eat foods. The standard microbiological method for L. monocytogenes detection in foods (ISO 11290-1: 1996 (ISO, International Organization for Standardization)) is cost and time consuming. Developments of rapid, cost-effective and automated diagnostic methods to detect food-borne pathogens in foods continue to be a major concern for the industry and public health. The aim of this study was the development of a rapid, sensitive and specific molecular detection method for L. monocytogenes. To this purpose, we have applied a capillary electrophoresis method to a PCR protocol (PCR-EES (EES, experion automated electrophoresis system)) for detecting L. monocytogenes in food. In particular, a microfluidic chip-based automated electrophoresis system (experion automated electrophoresis system, Bio-Rad Laboratories, USA) was used for the rapid and automatic analysis of the amplicons. Fifty naturally contaminated samples were analysed with this method and the results were compared with those obtained with ISO method. Moreover, the microfluidic chip-based automated electrophoresis system was compared with classical gel electrophoresis (PCR-CGE). The results showed that after 24 h of culture enrichment, the PCR-EES showed a relative accuracy of 100% with ISO, while using PCR-CGE decreased it down to 96%. After 48 h of enrichment, both PCR-EES and PCR-CGE showed an accuracy of 100% with ISO.

Listeria monocytogenes growth can be controlled on ready-to-eat meats through the incorporation of antimicrobial ingredients into the formulation or by postlethality kill steps. However, alternate approaches are needed to provide options that reduce sodium content but maintain protection against pathogen growth in meats after slicing. The objective of this study was to determine the inhibition of L. monocytogenes by propionic acid-based ingredients in high-moisture, cured turkey stored at 4 or 7°C. Six formulations of sliced, cured (120 ppm of NaNO2 ), deli-style turkey were tested, including control without antimicrobials, 3.2% lactate-diacetate blend (LD), 0.4% of a liquid propionate-benzoate-containing ingredient, or 0.3, 0.4, and 0.5% of a liquid propionate-containing ingredient. Products were inoculated with 5 log CFU L. monocytogenes per 100-g package (3 log CFU/ml rinsate), vacuum-sealed, and stored at 4 or 7°C for up to 12 weeks; and populations were enumerated by plating on modified Oxford agar. As expected, the control without antimicrobials supported rapid growth, with >2 log average per ml rinsate increase within 4 weeks of storage at 4°C, whereas growth was observed at 6 weeks for the LD treatment. For both replicate trials, all treatments that contained liquid propionate or propionate-benzoate limited L. monocytogenes growth to an increase of 1-log increase) was observed in individual samples for all propionate-containing treatments at weeks 10, 11, and 12. As expected, L. monocytogenes grew more rapidly when products were stored at 7°C, but trends in relative inhibition were similar to those observed at 4°C. These results verify that propionate-based ingredients inhibit growth of L. monocytogenes on sliced, high-moisture, cured turkey and can be considered as an alternative to reduce sodium-based salts while maintaining food safety.

In this study, the efficacy of UV-C treatment was determined on the reduction of foodborne pathogens on artificially contaminated frozen food surfaces. At first, the UV-C inactivation rates on 100 μl of the respective cocktails of Escherichia coli O157:H7, Salmonella , and Listeria monocytogenes covered underneath 0.5-cm-thick ice were examined. Simultaneously, the energy percentage of UV-C transmitted through the ice was determined. The experiments showed that more than 65% of the UV-C light energy passed through the ice and that UV-C susceptibility was in the descending order of E. coli O157:H7, Salmonella , and L. monocytogenes . L. monocytogenes , the most UV-C-resistant strain, was then selected to test on frozen raspberries. The UV-C inactivation kinetic data of L. monocytogenes were well described using the Weibull equation. During 720 s of UV-C exposure, with a total dose of 7.8 × 10(2) mJ/cm(2), a 1.5-log CFU/g reduction of L. monocytogenes population on the surface of frozen red raspberries was noted. No significant differences in total anthocyanins, total phenolics, and total antioxidant activity were observed between UV-C-treated and untreated frozen berries immediately after treatment. At the end of 9 months of storage at -35°C, UV-C-treated berries had statistically lower total phenolics, higher total anthocyanins, and similar total antioxidant activity compared with untreated berries. This study shows that UV-C light can be used to reduce the L. monocytogenes population on frozen raspberries.

Listeria monocytogenes CCUG 15526 was inoculated at a concentration of approximately 7.0 log(10) cfu/mL in milk samples with 0.3, 3.6, 10, and 15% fat contents. Milk samples with 0.3 and 3.6% fat content were also inoculated with a lower load of approximately 3.0 log(10) cfu/mL. Inoculated milk samples were subjected to a single cycle of ultra-high-pressure homogenization (UHPH) treatment at 200, 300, and 400 MPa. Microbiological analyses were performed 2 h after the UHPH treatments and after 5, 8, and 15 d of storage at 4 degrees C. Maximum lethality values were observed in samples treated at 400 MPa with 15 and 10% fat (7.95 and 7.46 log(10) cfu/mL), respectively. However, in skimmed and 3.6% fat milk samples, complete inactivation was not achieved and, during the subsequent 15 d of storage at 4 degrees C, L. monocytogenes was able to recover and replicate until achieving initial counts. In milk samples with 10 and 15% fat, L. monocytogenes recovered to the level of initial counts only in the milk samples treated at 200 MPa but not in the milk samples treated at 300 and 400 MPa. When the load of L. monocytogenes was approximately 3.0 log(10) cfu/mL in milk samples with 0.3 and 3.6% fat, complete inactivation was not achieved and L. monocytogenes was able to recover and grow during the subsequent cold storage. Fat content increased the maximum temperature reached during UHPH treatment; this could have contributed to the lethal effect achieved, but the amount of fat of the milk had a stronger effect than the temperature on obtaining a higher death rate of L. monocytogenes.

Full Text Available Controlling the food-borne pathogen Listeria (L. monocytogenes is of great importance from a food safety perspective, and thus for human health. The consequences of failures in this regard have been exemplified by recent large listeriosis outbreaks in the USA and Europe. It is thus particularly notable that tolerance to quaternary ammonium compounds such as benzalkonium chloride (BC has been observed in many L. monocytogenes strains. However, the molecular determinants and mechanisms of BC tolerance of L. monocytogenes are still largely unknown. Here we describe Tn6188, a novel transposon in L. monocytogenes conferring tolerance to BC. Tn6188 is related to Tn554 from Staphylococcus (S. aureus and other Tn554-like transposons such as Tn558, Tn559 and Tn5406 found in various Firmicutes. Tn6188 comprises 5117 bp, is integrated chromosomally within the radC gene and consists of three transposase genes (tnpABC as well as genes encoding a putative transcriptional regulator and QacH, a small multidrug resistance protein family (SMR transporter putatively associated with export of BC that shows high amino acid identity to Smr/QacC from S. aureus and to EmrE from Escherichia coli. We screened 91 L. monocytogenes strains for the presence of Tn6188 by PCR and found Tn6188 in 10 of the analyzed strains. These isolates were from food and food processing environments and predominantly from serovar 1/2a. L. monocytogenes strains harboring Tn6188 had significantly higher BC minimum inhibitory concentrations (MICs (28.5 ± 4.7 mg/l than strains without Tn6188 (14 ± 3.2 mg/l. Using quantitative reverse transcriptase PCR we could show a significant increase in qacH expression in the presence of BC. QacH deletion mutants were generated in two L. monocytogenes strains and growth analysis revealed that ΔqacH strains had lower BC MICs than wildtype strains. In conclusion, our results provide evidence that Tn6188 is responsible for BC tolerance in various L

Listeria monocytogenes has been detected in fresh as well as dry and semidry fermented sausages, rendering preparation and consumption of these products as a potential risk to human health. The aims of this study were (1) to evaluate the L. monocytogenes prevalence in 288 fresh and 237 fermented sausages produced in northern Italy; (2) to quantify the average pathogen Most Probable Number (MPN) per g of sausage; (3) to evaluate the sausage strain genetic diversity by automated PvuII ribotyping; and (4) to predict the pathogenicity lineage of these isolates determining their DuPont Identification Library Codes (DUP-IDs) by EcoRI ribotyping. The overall prevalence of L. monocytogenes in the sampled sausages was 28.2%. The percentage of L. monocytogenes positive fresh sausages was significantly higher than that of fermented sausages (i.e. 38.9 vs 15.2%), which had a pathogen load always lower than 10 MPN/g. In contrast, 16.1% of fresh sausages were contaminated by 10 to 100 MPN/g and 20.5% had more than 100 MPN/g. PvuII successfully discriminated sausage isolates with a Simpson's numerical index of discrimination of 0.637. A total of 12 and 9 different PvuII ribogroups were identified among 47 fresh and 24 fermented randomly selected sausage strains, respectively. Six of those ribogroups were shared between strains contaminating both kinds of sausages. According to the evaluation of the strain DUP-IDs, the majority of the isolates investigated in this study were part of the type II L. monocytogenes pathogenicity lineage, but type I lineage strains were identified among fermented sausage isolates. In conclusion, L. monocytogenes prevalence in Italian sausages was estimated to be around 28.2%. However, 84.2% of the samples were contaminated by less than 100 MPN of L. monocytogenes per g and the majority of L. monocytogenes contaminating strains would be classified in the type II pathogenicity lineage, including serotypes 1/2a, 1/2c and 3a.

In the past years, there has been a particular focus on the application of bacteriocins produced by lactic acid bacteria (LAB) in controlling the growth of pathogenic bacteria in foods. The aim of this study was to select LAB strains with antimicrobial activity, previously isolated from a traditional Azorean artisanal cheese (Pico cheese), in order to identify those with the greatest potential in reducing Listeria monocytogenes in fresh cheese. Eight bacteriocin producer strains identified as Lactococcus lactis (1) and Enterococcus faecalis (7) were tested. In general, the bacteriocin-producing strains presented a moderate growth in fresh cheese at refrigeration temperatures (4 °C), increasing one log count in three days. They exhibited slow acidification capacity, despite the increased production of lactic acid displayed by some strains after 24h. Bacteriocin activity was only detected in the whey of fresh cheese inoculated with two Enterococcus strains, but all cheeses made with bacteriocin-producing strains inhibited L. monocytogenes growth in the agar diffusion bioassay. No significant differences were found in overall sensory evaluation made by a non-trained panel of 50-52 tasters using the isolates as adjunct culture in fresh cheese, with the exception of one Enterococcus strain. To test the effect of in situ bacteriocin production against L. monocytogenes, fresh cheese was made from pasteurized cows' milk inoculated with bacteriocin-producing LAB and artificially contaminated with approximately 10(6) CFU/mL of L. monocytogenes. The numbers of L. monocytogenes were monitored during storage of fresh cheese at refrigeration temperature (4 °C) for up to 15 days. All strains controlled the growth of L. monocytogenes, although some Enterococcus were more effective in reducing the pathogen counts. After 7 days, this reduction was of approximately 4 log units compared to the positive control. In comparison, an increase of 4 log CFU/mL in pathogen numbers was

After more than 20 years of work with discussing the setting of microbiological criteria for Listeria monocytogenes in foods, Codex Alimentarius on Food Hygiene has finalised a proposal that was recently adopted by the Codex Alimentarius Commission. The effort of developing procedures for making...... the microbiological criteria risk-based to the greatest extent possible has challenged scientists and managers during this long time period. Yet, the establishment of microbiological criteria for L. monocytogenes is still being discussed and several approaches are possible. Setting of microbiological criteria...

Nineteen Listeria monocytogenes strains were characterized by automated ribotyping, pulsed-field gel electrophoresis, and plasmid profiling to determine the relationship between genotype and sanitizer resistance. Isolates within a ribogroup had a consistent sensitivity or resistance phenotype except for ribogroup C isolates. All isolates with resistance phenotypes harbored two plasmids. The sensitivity of L. monocytogenes strains to quaternary ammonium compounds (QACs) was correlated with sensitivity to sanitizers and antibiotics with other modes of action. All isolates tested contained the mdrL gene, which encodes an efflux pump that confers resistance to QACs and is both chromosome and plasmid borne.

Controlling the food-borne pathogen Listeria (L.) monocytogenes is of great importance from a food safety perspective, and thus for human health. The consequences of failures in this regard have been exemplified by recent large listeriosis outbreaks in the USA and Europe. It is thus particularly notable that tolerance to quaternary ammonium compounds such as benzalkonium chloride (BC) has been observed in many L. monocytogenes strains. However, the molecular determinants and mechanisms of BC tolerance of L. monocytogenes are still largely unknown. Here we describe Tn6188, a novel transposon in L. monocytogenes conferring tolerance to BC. Tn6188 is related to Tn554 from Staphylococcus (S.) aureus and other Tn554-like transposons such as Tn558, Tn559 and Tn5406 found in various Firmicutes. Tn6188 comprises 5117 bp, is integrated chromosomally within the radC gene and consists of three transposase genes (tnpABC) as well as genes encoding a putative transcriptional regulator and QacH, a small multidrug resistance protein family (SMR) transporter putatively associated with export of BC that shows high amino acid identity to Smr/QacC from S. aureus and to EmrE from Escherichia coli. We screened 91 L. monocytogenes strains for the presence of Tn6188 by PCR and found Tn6188 in 10 of the analyzed strains. These isolates were from food and food processing environments and predominantly from serovar 1/2a. L. monocytogenes strains harboring Tn6188 had significantly higher BC minimum inhibitory concentrations (MICs) (28.5 ± 4.7 mg/l) than strains without Tn6188 (14 ± 3.2 mg/l). Using quantitative reverse transcriptase PCR we could show a significant increase in qacH expression in the presence of BC. QacH deletion mutants were generated in two L. monocytogenes strains and growth analysis revealed that ΔqacH strains had lower BC MICs than wildtype strains. In conclusion, our results provide evidence that Tn6188 is responsible for BC tolerance in various L. monocytogenes

The in vitro inhibitory activity of enterocin-35 produced by Enterococcus faecium CRL 35, was studied against Listeria monocytogenes, isolated from seafoods. Optimal growth conditions of the enterocin-35 producing strain, for higher bacteriocin production and improve the extraction and purification of these peptides, were applied. A crude extract of enterocin-35 was assayed in a frozen seafood artificially contaminated with Listeria monocytogenes isolate, simulating at laboratory scale an eventual application of this biopreservant in a routine production process at factory level. The feasibility of biopreservation of seafoods by means of bacteriocins is proposed and discussed.

Experimental conditions can affect the outcome of bacterial stress-tolerance assays. Growth conditions that optimize microbial recovery should be established to help evaluate the effectiveness of treatment conditions for food safety. The objectives of this study were to determine the effects of growth and recovery temperatures on pressure resistance of early stationary-phase Listeria monocytogenes in milk. The tested conditions were the following: (1) L. monocytogenes was grown at various temperatures (10, 15, 20, 25, 30, 35, 40 and 43 degrees C), suspended in ultra-high temperature (UHT) -processed whole milk, pressure-treated at 400 MPa for 2 min at 21 degrees C and recovered on Tryptic Soy Agar supplemented with 0.6% yeast extract (TSAYE) at 35 degrees C; (2) L. monocytogenes was grown at 35 and 43 degrees C, pressure treated in milk (400 and 500 MPa, respectively, for 2 min at 21 degrees C) and recovered on TSAYE at various temperatures (4, 10, 15, 20, 25, 30, 35 and 40 degrees C); (3) L. monocytogenes originally grown at 35 degrees C, was pressure treated in milk (400 or 450 MPa for 2 min at 21 degrees C), and recovered on TSAYE at 10 degrees C for various time intervals (1, 2, 3, 6, 9 and 12 days) then at 35 degrees C for 5 days. There was no significant difference (P>0.05) in pressure-resistance of L. monocytogenes grown at 10 to 25 degrees C with approximately 6.5-log CFU/ml population reductions. At growth temperatures greater than 25 degrees C, pressure resistance increased with less than 1-log CFU/ml reduction observed for L. monocytogenes originally grown at 43 degrees C. After pressure treatment, regardless of growth temperature and pressure treatment, the greatest recovery of L. monocytogenes was within the 4 to 20 degrees C range; maximum recovery at 10 degrees C required approximately 24 days. The time for comparable post-pressure treatment recovery could be reduced by incubation at 10 degrees C for at least 2 days followed by incubation at 35

The lmaA gene of Listeria monocytogenes encodes a protein capable of inducing delayed-type hypersensitivity reactions in L. monocytogenes-immune mice (S. Göhmann, M. Leimeister-Wachter, E. Schiltz, W. Goebel, and T. Chakraborty, M. Microbiol. 4:1091-1099, 1990). Here we show that it is the last gene of the lma operon, which now comprises four genes, lmaDCBA. Maxicell analysis of peptides encoded by the lma operon identified four polypeptides of 16.7, 16.4, 14.9, and 21 kDa which correspond to...

The foodborne bacterial pathogen, Listeria monocytogenes, commonly contaminates foods during processing, where the microorganisms are potentially subjected to low relative humidity (RH) conditions for extended periods of time. The objective of this study was to examine survival during desiccation...... (43% RH and 15°C) of biofilm L. monocytogenes N53-1 cells on stainless steel coupons and to assess subsequent transfer to salmon products. Formation of static biofilm (2days at 100% RH and 15°C) prior to desiccation for 23days significantly (P...

The presence of multiple species of Listeria in regulated food products is not uncommon and can complicate the recovery of Listeria monocytogenes particularly on a non-differentiating medium. The potential complications of Listeria seeligeri and Listeria welshimeri on the recovery of L. monocytogenes from inoculated food test samples using the U.S. Food and Drug Administration's (FDA) selective enrichment procedure was investigated. Post-enrichment enumeration, in the absence of food product, indicates that some L. seeligeri and L. monocytogenes pairings may have population differentials as great as 2.7 ± 0.1 logs with L. seeligeri being the predominant species. A similar observation was noted for L. welshimeri and L. monocytogenes pairings which resulted in population differentials as large as 3.7 ± 0.2 logs with L. welshimeri being the predominant species. Select strain pairings were used to inoculate guacamole, crab meat, broccoli, and cheese with subsequent recovery by the FDA Bacteriological Analytical Manual (BAM) method with 10 colonies per sample selected for confirmation. The presence of L. seeligeri had little effect on the recovery of L. monocytogenes. The presence of L. welshimeri resulted in the failure to recover L. monocytogenes in three out of the four food matrices. This work extends the observation that non-pathogenic species of Listeria can complicate the recovery of L. monocytogenes and that competition during selective enrichment is not limited to the presence of just Listeria innocua. Published by Elsevier Ltd.

Strain CS526 was isolated from frozen surimi and identified as a bacteriocin producer that had strong inhibitory activity against Listeria monocytogenes. Strain CS526 was identified as Carnobacterium piscicola by partial 16S rDNA sequence similarity. The ability of this bacteriocinogenic strain and nonbacteriocinogenic C. piscicola JCM5348 to inhibit the growth of L. monocytogenes was examined in culture broth incubated at 12 degrees C and cold-smoked salmon stored at 4, 12, and 20 degrees C. L. monocytogenes viable counts in the culture broth rapidly declined from 10(6) colony-forming units per ml to less than 10 colony-forming units per ml within 1 day at 12 degrees C in the presence of C. piscicola CS526. At 4 and 12 degrees C, inhibition of L. monocytogenes on salmon depended on the initial inoculum level of C. piscicola CS526. However, C. piscicola CS526 was bactericidal to L. monocytogenes within 21 and 12 days at 4 and 12 degrees C in cold-smoked salmon, respectively, even when the initial inoculum levels were low. C. piscicola CS526 suppressed the maximum cell number of L. monocytogenes by two and three log cycles, even at 20 degrees C. However, C. piscicola JCM5348 did not prevent the growth of the pathogen, except at 4 degrees C. Bacteriocin was detected in the samples coinoculated with C. piscicola CS526. The study shows that C. piscicola CS526 might have potential for biopreservation of refrigerated foods against L. monocytogenes.

The presence of multiple species of Listeria in regulated food products is not uncommon and can complicate the recovery of Listeria monocytogenes particularly on a non-differentiating medium. The potential complications of Listeria seeligeri and Listeria welshimeri on the recovery of L. monocytogenes from inoculated food test samples using the U.S. Food and Drug Administration's (FDA) selective enrichment procedure was investigated. Post-enrichment enumeration, in the absence of food product, indicates that some L. seeligeri and L. monocytogenes pairings may have population differentials as great as 2.7 ± 0.1 logs with L. seeligeri being the predominant species. A similar observation was noted for L. welshimeri and L. monocytogenes pairings which resulted in population differentials as large as 3.7 ± 0.2 logs with L. welshimeri being the predominant species. Select strain pairings were used to inoculate guacamole, crab meat, broccoli, and cheese with subsequent recovery by the FDA Bacteriological Analytical Manual (BAM) method with 10 colonies per sample selected for confirmation. The presence of L. seeligeri had little effect on the recovery of L. monocytogenes. The presence of L. welshimeri resulted in the failure to recover L. monocytogenes in three out of the four food matrices. This work extends the observation that non-pathogenic species of Listeria can complicate the recovery of L. monocytogenes and that competition during selective enrichment is not limited to the presence of just Listeria innocua. PMID:25475325

The critical roles of sortase A (SrtA) and listeriolysin O (LLO) in Listeria monocytogenes pathogenicity render these two virulence factors as ideal targets for the development of anti-virulence agents against L. monocytogenes infection. Additionally, the structures of SrtA and LLO are highly conserved among the members of sortase enzyme family and cholesterol dependent toxin family. Here, phloretin, a natural polyphenolic compound derived from apples and pears that has little anti-L. monocytogenes activity, was identified to simultaneously inhibit LLO expression and neutralize SrtA catalytic activity. Phloretin neutralized SrtA activity by causing a conformational change in the protein's active pocket, which prevented engagement with its substrate. Treatment with phloretin simultaneously reduced L. monocytogenes invasion into host cells and blocked the escape of vacuole-entrapped L. monocytogenes into cytoplasm. Further, L. monocytogenes-infected mice that received phloretin showed lower mortality, decreased bacterial burden and reduced pathological injury. Our results demonstrate that phloretin is a promising anti-infective therapeutic for infections caused by L. monocytogenes due to its simultaneous targeting of SrtA and LLO, which may result in fewer side effects than those caused by other antibiotics.

The luxS gene involved in quorum sensing has been shown to control different behaviour of probiotic lactobacilli. In this study we investigated if luxS in Lactobacillus acidophilus NCFM was up-regulated in response to Listeria monocytogenes EGD-e. The two bacterial strains were grown in mono- and co-culture and the growth of both bacteria and the transcriptional level of luxS in L. acidophilus cells were monitored. Contrary to L. acidophilus, the growth of L. monocytogenes was significantly affected by co-cultivation. Transcriptional analysis showed that the expression of luxS increased during exponential growth in L. acidophilus cells with the highest level in the late-exponential growth phase, decreasing in the stationary phase. Following co-cultivation with L. monocytogenes, the transcriptional level of luxS increased significantly in mid-exponential growing cells of L. acidophilus after incubation with viable L. monocytogenes cells and by addition of cell-free culture supernatant of L. monocytogenes, whereas incubation with heat killed cells of L. monocytogenes had no effect on the transcriptional level. This could indicate that the up-regulation of luxS is due to a response to a secreted compound produced by L. monocytogenes cells.

Riboswitches are ligand-binding elements located in 5' untranslated regions of messenger RNAs, which regulate expression of downstream genes. In Listeria monocytogenes, a vitamin B12-binding (B12) riboswitch was identified, not upstream of a gene but downstream, and antisense to the adjacent gene, pocR, suggesting it might regulate pocR in a nonclassical manner. In Salmonella enterica, PocR is a transcription factor that is activated by 1,2-propanediol, and subsequently activates expression of the pdu genes. The pdu genes mediate propanediol catabolism and are implicated in pathogenesis. As enzymes involved in propanediol catabolism require B12 as a cofactor, we hypothesized that the Listeria B12 riboswitch might be involved in pocR regulation. Here we demonstrate that the B12 riboswitch is transcribed as part of a noncoding antisense RNA, herein named AspocR. In the presence of B12, the riboswitch induces transcriptional termination, causing aspocR to be transcribed as a short transcript. In contrast, in the absence of B12, aspocR is transcribed as a long antisense RNA, which inhibits pocR expression. Regulation by AspocR ensures that pocR, and consequently the pdu genes, are maximally expressed only when both propanediol and B12 are present. Strikingly, AspocR can inhibit pocR expression in trans, suggesting it acts through a direct interaction with pocR mRNA. Together, this study demonstrates how pocR and the pdu genes can be regulated by B12 in bacteria and extends the classical definition of riboswitches from elements governing solely the expression of mRNAs to a wider role in controlling transcription of noncoding RNAs.

Listeriosis outbreaks have been associated with a variety of foods. This study investigated the prevalence and diversity of Listeria monocytogenes and Listeria spp. in ready-to-eat (RTE) products and evaluated the performance of a rapid detection method, the 3M molecular detection assay for L. monocytogenes (MDA-LM), for detection of L. monocytogenes. Assay results were compared with those obtained using the U.S. Food and Drug Administration standard culture method described in the Bacteriological Analytical Manual. Products (n = 200) were purchased from retail stores: 122 aquatic products, 22 products of animal origin, 18 vegetarian products, 15 deli meat products, 13 salad and vegetable products, 4 desserts, 2 egg-based products, and 4 other products. L. monocytogenes prevalence was comparable with both methods. Overall, 15 (7.5%) of 200 samples were positive for L. monocytogenes: 3% of aquatic products, 1.5% of products of animal origin, 1% of vegetarian products, and 2% of deli meat products. Compared with the standard culture method, the sensitivity, specificity, and the accuracy of the MDA-LM were 86.7% (95% confidence interval, 58.4 to 97.7%), 98.4% (95% confidence interval, 95.0 to 99.6%), and 97.5%, respectively. Using the culture-based method, 18 (9%) of 200 samples were positive for Listeria species other than L. monocytogenes. Listeria isolates from these samples were classified into nine allelic types (ATs). The majority of isolates were classified as ATs 58 and 74, which were identified as L. monocytogenes lineages I and IV, respectively. Listeria innocua and Listeria welshimeri also were represented by isolates of multiple ATs. The MDA-LM is a rapid and reliable technique for detecting L. monocytogenes in various RTE foods. Further study is needed to develop effective control strategies to reduce L. monocytogenes contamination in RTE foods.

Listeria monocytogenes is responsible for the life-threatening food-borne disease listeriosis. This disease mainly affects elderly and immunocompromised individuals, causing bacteremia and meningoencephalitis. In pregnant women, L. monocytogenes infection leads to abortion and severe infection of the fetus or newborn. The L. monocytogenes intracellular life cycle is critical for pathogenesis. Previous studies have established that the major virulence factor of L. monocytogenes, the pore-forming toxin listeriolysin O (LLO), is sufficient to induce L. monocytogenes internalization into human epithelial cell lines. This internalization pathway strictly requires the formation of LLO pores in the plasma membrane and can be stimulated by the heterologous pore-forming toxin pneumolysin, suggesting that LLO acts nonspecifically by forming transmembrane pores. The present work tested the hypothesis that Ca2+ and K+ fluxes subsequent to perforation by LLO control L. monocytogenes internalization. We report that L. monocytogenes perforates the host cell plasma membrane in an LLO-dependent fashion at the early stage of invasion. In response to perforation, host cells undergo Ca2+ -dependent but K+ -independent resealing of their plasma membrane. In contrast to the plasma membrane resealing process, LLO-induced L. monocytogenes internalization requires both Ca2+ and K+ fluxes. Further linking ion fluxes to bacterial internalization, treating cells with a combination of Ca2+ and K+ ionophores but not with individual ionophores is sufficient to induce efficient internalization of large cargoes, such as 1-μm polystyrene beads and bacteria. We propose that LLO-induced L. monocytogenes internalization requires a Ca2+ - and K+ -dependent internalization pathway that is mechanistically distinct from the process of plasma membrane resealing.

A stochastic model was developed for simultaneous growth of low numbers of Listeria monocytogenes and populations of lactic acid bacteria from the aroma producing cultures applied in cottage cheese. During more than two years, different batches of cottage cheese with aroma culture were analysed for pH, lactic acid concentration and initial concentration of lactic acid bacteria. These data and bootstrap sampling were used to represent product variability in the stochastic model. Lag time data were estimated from observed growth data (lactic acid bacteria) and from literature on L. monocytogenes single cells. These lag time data were expressed as relative lag times and included in growth models. A stochastic model was developed from an existing deterministic growth model including the effect of five environmental factors and inter-bacterial interaction [Østergaard, N.B, Eklöw, A and Dalgaard, P. 2014. Modelling the effect of lactic acid bacteria from starter- and aroma culture on growth of Listeria monocytogenes in cottage cheese. International Journal of Food Microbiology. 188, 15-25]. Growth of L. monocytogenes single cells, using lag time distributions corresponding to three different stress levels, was simulated. The simulated growth was subsequently compared to growth of low concentrations (0.4-1.0 CFU/g) of L. monocytogenes in cottage cheese, exposed to similar stresses, and in general a good agreement was observed. In addition, growth simulations were performed using population relative lag time distributions for L. monocytogenes as reported in literature. Comparably good predictions were obtained as for the simulations performed using lag time data for individual cells of L. monocytogenes. Therefore, when lag time data for individual cells are not available, it was suggested that relative lag time distributions for L. monocytogenes can be used as a qualified default assumption when simulating growth of low concentrations of L. monocytogenes.

Postprocessing contamination in processing plants has historically been a significant source of Listeria monocytogenes in ready-to-eat delicatessen meats, and therefore a major cause of human listeriosis cases and outbreaks. Recent risk assessments suggest that a majority of human listeriosis cases linked to consumption of contaminated deli meats may be due to L. monocytogenes contamination that occurs at the retail level. To better understand the ecology and transmission of Listeria spp. in retail delicatessens, food and nonfood contact surfaces were tested for L. monocytogenes and other Listeria spp. in a longitudinal study conducted in 30 retail delis in three U.S. states. In phase I of the study, seven sponge samples were collected monthly for 3 months in 15 delis (5 delis per state) prior to start of daily operation; in phase II, 28 food contact and nonfood contact sites were sampled in each of 30 delis during daily operation for 6 months. Among the 314 samples collected during phase I, 6.8% were positive for L. monocytogenes. Among 4,503 samples collected during phase II, 9.5% were positive for L. monocytogenes; 9 of 30 delis showed low L. monocytogenes prevalence (Listeria spp. isolates, including 184 Listeria innocua, 48 Listeria seeligeri, and 13 Listeria welshimeri were characterized. Pulsed-field gel electrophoresis (PFGE) was used to characterize 446 L. monocytogenes isolates. PFGE showed that for 12 of 30 delis, one or more PFGE types were isolated on at least three separate occasions, providing evidence for persistence of a given L. monocytogenes subtype in the delis. For some delis, PFGE patterns for isolates from nonfood contact surfaces were distinct from patterns for occasional food contact surface isolates, suggesting limited cross-contamination between these sites in some delis. This study provides longitudinal data on L. monocytogenes contamination patterns in retail delis, which should facilitate further development of control strategies in

This study aimed to evaluate the occurrence of Listeria monocytogenes in cheese and in the environment of three small-scale dairy plants (A, B, C) located in the Northern region state of São Paulo, Brazil, and to characterize the isolates using conventional serotyping and PFGE. A total of 393 samples were collected and analyzed from October 2008 to September 2009. From these, 136 came from dairy plant A, where only L. seeligeri was isolated. In dairy plant B, 136 samples were analyzed, and L. innocua, L. seeligeri and L. welshimeri were isolated together with L. monocytogenes. In dairy plant C, 121 samples were analyzed, and L. monocytogenes and L. innocua were isolated. Cheese from dairy plants B and C were contaminated with Listeria spp, with L. innocua being found in Minas frescal cheese from both dairy plants, and L. innocua and L. monocytogenes in Prato cheese from dairy plant C. A total of 85 L. monocytogenes isolates were classified in 3 serotypes: 1/2b, 1/2c, and 4b, with predominance of serotype 4b in both dairy plants. The 85 isolates found in the dairy plants were characterized by genomic macrorestriction using ApaI and AscI with Pulsed Field Gel Electrophoresis (PFGE). Macrorestriction yielded 30 different pulsotypes. The presence of indistinguishable profiles repeatedly isolated during a 12-month period indicated the persistence of L. monocytogenes in dairy plants B and C, which were more than 100 km away from each other. Brine used in dairy plant C contained more than one L. monocytogenes lineage. The routes of contamination were identified in plants B and C, and highlighted the importance of using molecular techniques and serotyping to track L. monocytogenes sources of contamination, distribution, and routes of contamination in dairy plants, and to develop improved control strategies for L. monocytogenes in dairy plants and dairy products.

Seafood salad has been identified as a ready-to-eat food with a relatively high incidence of contamination by Listeria monocytogenes; however, little is known about the behavior of this pathogen in seafood salad as a function of product pH and storage temperature. To produce data towards the development of a predictive growth model, a 6-strain cocktail of L. monocytogenes was inoculated onto the surface of a shrimp-crabmeat product, mixed with mayonnaise that was previously adjusted with NaOH to pH 3.7, 4.0, 4.4, 4.7 or 5.1, and then stored at 4 degrees , 8 degrees or 12 degrees C under both aerobic and vacuum conditions. At each storage temperature, L. monocytogenes was able to grow in the seafood salad under both aerobic and vacuum conditions. The slowest growth of L. monocytogenes was observed in seafood salad with a mayonnaise pH of 3.7 and a storage temperature of 4 degrees C under vacuum condition. In salad with the same mayonnaise pH, the growth rate (GR, log10 cfu/h) of L. monocytogenes increased as a function of storage temperature. At the same storage temperature, the lag phase duration (LPD, h) of L. monocytogenes decreased as mayonnaise pH increased. At the same mayonnaise pH and temperature, LPD of L. monocytogenes was greater under aerobic than under vacuum conditions. Regression analyses indicated that mayonnaise pH is the main effector on the LPD of L. monocytogenes in seafood salad, and storage temperature was the main effector on the GR. Secondary models that describe LPD and GR of L. monocytogenes in seafood salad as a function of mayonnaise pH and storage temperature were produced.